For 16 years Dr. Hines didn’t run Ads on this site. Readers sent him sufficient donations to pay the bills that keep this website on the internet. But in 2017, Google informed him that his website needed to be reprogrammed to be “mobile-friendly”. You see, times have changed: Today, 82% of his readers view the articles on smart phones and tablets. Less than 20% do on full size personal computers like his. PCs are less common now but days are still only 24 hours long. If he took the time to redesign all his webpages he wouldn't have time to update or write new ones - let alone care for the animals that depend on him. His hope is that these ads (selected by Google, not him) will generate enough revenue to have others make the website coding changes for him that Google desires.
There was a time when infectious diseases were the leading cause of mortality in our dogs and cats. We have good, long-lasting vaccines now so those times have passed. Today, chronic kidney disease leading to kidney failure is near the top of the list as the cause of death in older pets. Just behind the #1 and #2 causes in dogs - cancer and heart disease – and probably ahead of heart disease in cats.
Not every pet with kidney disease has age-related kidney decline. A few dogs carry genetic diseases that cause their kidneys to fail at about 1-3 years of age. The kidneys of cats that inherited polycystic kidney disease often fail in midlife (ref) A tendency to form kidney stones can also destroy the kidneys. (ref1, ref2) So can exposure to dietary toxins (eg antifreeze, aflatoxins). In others, unfortunate reactions to medications are to blame and, a few, autoimmune disorders. (ref), and perhaps some to infectious organisms like leptospirosis. (ref1, ref2)
But for the vast majority of our pets, kidney failure is a disease of old age. By the time a dog reaches ten, about 15% show laboratory test evidence that their kidneys have lost some of their capacity to cleanse their body. In 10-year-old cats, those chances are even higher. By the time house cats reach the age of 15, perhaps 15– 30% of them have some decline in their kidney function. Vets used to just call it glomerulosclerosis. Today we call it CKD (chronic kidney disease) or CRD (chronic renal (=kidney) disease (CRD) or chronic tubulointerstitial nephritis. All synonyms for a slow, relentless, age-related inflammation that slowly destroys your pet’s individual kidney filter units, the nephrons. (ref) (You might notice that the less doctors understand about a problem, the more complicated names they tend to give it.)
Old age brings multiple health issues to all of us. But only some of our cats and dogs will reach the point of actual kidney failure. For most, unrelated heath issues will cause them to eventually pass away. (ref) Organs of your dog or cat’s body have to work in unison to keep each other functioning well. So although you may have been told that your pet died of heart failure, or perhaps and infection, its kidney issues may have contributed to its demise. (ref1, ref2)
The 2016 Merck veterinary manual states that chronic kidney disease (CKD) affects as many as 10% of dogs and 35% of cats during their lifetimes. In dogs and cats that are fortunate enough to reach old age, the numbers with the problem is considerably larger. God generously gave all mammals considerably more of those nephron filter units that required. Us humans have about 1 million nephron filter units in each of our kidneys. (ref) No one I know of has estimated their number in dogs or cats. With every heartbeat, about 20-25% of your dog or cat’s heart volume of blood is sent to the pet’s kidneys for cleansing, fluid regulation and blood ion adjustments.
Do Veterinarians Know Much More About Why The Kidneys Of Elderly Cats And Dogs Fail Than They Did 10 Years Ago ?
Why it is that the kidneys of old dogs and old cats commonly fail remains unknown. There are oodles of theories. All remain unproven. Veterinarians do not know if there is one major cause or many causes. We also know very little about the dynamic events (real time processes) occurring in a pet’s kidneys that lead to their eventual failure. What we do know is that by the time kidneys fail, they all look pretty much the same when viewed under a microscope. The glomeruli (the numerous small filters that clean the blood) are scarred to the point that they no longer work and there is usually evidence of inflammation surrounding them. The term for that scarring is glomerulosclerosis. Microscopically it is unmistakable. It is irreversible and some pathologists viewing those slides call it no more than the end stage wreckage of what once were once healthy kidneys.
Unfortunately, much of what you will read online is an echo chamber of supposition, guesswork and consensus statements based on data taken from conflicting human, rat, mouse, dog and cat kidney decline studies. Since veterinarians have little idea why kidney decline occurs in older pets, it is quite difficult for them to plan strategies to treat, slow or prevent the disease. That goes for all the medication, lifestyle changes and diets that your veterinarian hopes might slow the progression of CRD. It is one of the least understood areas of veterinary medicine.
The only studies that pass scientific muster were run years ago mostly in dogs but one in cats. Studies that would confirm those results in cats and dogs or look for effective medication can no longer be attempted in the Western world. They involved removing the majority of an animal’s kidneys and would be considered too cruel today. More current studies don’t pass muster because they have too many multiple confounding variables (ref) or too few animals to support the conclusions that they reached. In addition, companies with products to sell underwrite the costs of most of them – never a good situation for unbiased conclusions.
I’m left in that same data bind. That’s why I have procrastinated 5 years in writing this article, the SDMA test and Kidney Diets. The amount of information I had to mull over was enormous. The results of many of the studies conflict with one another. Results are all over the map. Most were never repeated or independently verified. When science collides with the opportunity to make money, science is rarely the winner. (ref1, ref2) Its not that money is not out there to run well-designed studies. Colgate-Palmolive, the parent company of Hills Prescription diets, had a 2017 revenue of 15.45 Billion dollars with 7.12 billion spent on advertising. Idexx revenues were 1.97 billion in 2017. But industry never tosses dice with uncertain outcomes when things are already going peachy.
So I had to bone up on what physicians have learned about diagnosing and treating CRD in their patients. Some are going to say the same thing I mentioned earlier: that one cannot trust that what works or doesn’t work in humans will work or not work in your dog or cat. That, to some extent is true -but it’s the best I can offer you. Human medical research is not free of shenanigans either. But the FDA and the NIH try to see to it that there is less of it.
The veterinary International Renal Interest Society (IRIS) periodically put out kidney disease treatment guidelines for dogs and cats. These guidelines are produced by specialists that have devoted their lives to attempting to understand kidney disease in dogs and cats. Unfortunately, suggested time points when medications need to begin, which ones are likely to help, which don’t and at what dose to use them are quite speculative. The same goes for their nutritional suggestions. Read them for cats here ,for dogs, here. How important kidney disease is in veterinary medicine today is reflected in the enormous number of articles written about it. Here are just a few of the more recent ones: (ref1, ref2, ref3, ref4, ref5)
If My Dog Or Cat Has Kidney Disease What Signs Might I See ?
The most common forms of kidney disease in dogs and cats take years to develop. During the earliest stages, you are unlikely to notice any changes in your cat or dog’s behavior or appearance. That is because, as I mentioned, the kidneys of dogs, cats and humans have large, built-in reserves – many more individual filtering units (=nephrons) than are required to cleanse the blood.
That early period is when your pet’s bloodwork results (“wellness exams, geriatric profiles”) give your vet little evidence that something is brewing. Normal cut off values for blood results are somewhat arbitrary. High-end normals can be just that – normal for your pet. They can also return to midline values the following day. But high-end values (particularly when they persist) often indicate a brewing problem. Few owners are going to repeat these tests every month to detect these trends. IRIS, the National Renal Interest Society, associates blood creatinine levels of 1.4 - 2.0 for dogs and 1.6 - 2.8 for cats with this early period. The pet’s early morning urine might be a bit too dilute as well (low specific gravity ). Albumin protein leaking into your pet’s urine might be beginning warning as well. (ref) IRIS2015.pdf If the SDMA test is specific enough to allow your vet to pick up on CKD earlier remains to be seen. Read about that here. SDMA2018.htm
A persistent increase in drinking and peeing (polyuria and polydipsia =PU/PD) in your pet) in the absence of another explanation (eg fever, diet change, hot weather, corticosteroids, diabetes, etc.) is often the earliest sign pet owners notice. Or, they might just notice that their pet is having more household potty accidents. The urine that these pets produce is very dilute (low specific gravity). Their bodies are running more fluid through the kidneys in an attempt to keep blood waste products and toxins levels down. Never ever deprive these pets of all the water they care to drink.
The next thing you might notice in your cat or dog is less energy, less curiosity and more sleep time. That often occurs along with a decreased appetite and more picky eating that results in a drop in your pet’s body weight. Owners are often surprised when I point that out. They reply that they just thought it comes with getting old. Early kidney problems can be mistaken for cognitive decline (CDS aka doggie Alzheimer’s); so its always a good idea to run a blood panel on dogs and cats facing memory issues. CKD and CCD can, and often do, coexist together. Some associate the weakness that comes with advancing kidney disease as due to low blood potassium levels (=hypokalema). Although that sometimes does occur, it is only a small part of the problem. (ACE-inhibiting blood pressure medicines like benazepril and ARBs that accomplish the same thing can actually cause potassium levels to be above normal = hyperkalemia).
As CKD progresses, decreased appetite causes almost all pets loose lean body weight. We are uncertain why dogs with advanced kidney disease loose their appetite, but it is almost certainly due in part to rising levels of metabolic wastes and toxins within their bodies (in doctorspeak: multifactorial metabolic derangements). In us humans, the loss of lean muscle mass to CKD is one of the best indicators of ones approaching mortality. (ref)
As CKD progresses, some dogs and cats begin to gag or vomit. We have no way to determine if pets experience nausea – but many folks attribute their vomiting and gagging that is sometimes seen in CKD to that. Others attribute it to stomach irritation (gastritis) caused by the uremic toxins and/or alterations in the pets body acidity (acid base balance). In advanced CKD cases, oral ulcers often occur.
It is common for pets with CRD to have gum (periodontal) disease. That needs to be tended to by your veterinarian. (remember, these pets are poor anesthetic risks (ref) Whether periodontal disease is the cause or result of kidney failure is still being debated. (ref1, ref2) But we do know that in CKD, kidneys of dogs and cats can no longer keep blood phosphorus levels in check. High body phosphorus levels in your pet leads to loss of bone calcium (secondary renal hyperparathyroidism). That in tern leads to loose teeth and periodontal disease. (ref)
CKD is a progressive disease. As it progresses, pets often become anemic. The build up of toxic waste products in the blood might explain a part of your pet’s lack of energy – but anemia - causing a lack of energy certainly does as well. You pet’s kidneys have multiple chores. Besides cleansing its blood, normal kidneys produce most of its EPO (erythropoietin). EPO is essential for the pet’s bone marrow to produce red blood cells. Kidney disease often lowers a pet’s ability to produce it (some continues to be produced in the liver). Picky eating also leads to malnutrition. That in itself can cause anemia – particularly if folic acid, vitamin B12 and iron are not absorbed in sufficient quantities. Although marked anemia causes paleness and a rapid pulse, the color of your pet’s tongue or its heart rate at a veterinary hospital is not a good judge of anemia. A PCV or RBC count is.
Anything that causes blood loss can cause anemia (eg bleeding, parasites). Your veterinarian has learned to look for clues that hint to the underlying cause. When bleeding or parasites are the cause, examinations show that your pet’s bone marrow is cranking out new red blood cells as fast as it can (a regenerative anemia). The anemia associated with CKD is non-regenerative. The pet’s bone marrow is neglecting the red blood cell formation process. (ref) The same bone marrow processes suppressed by CKD can lower a pet’s ability to generate thrombocyte as well. Thrombocytes play an important role in blood clotting. (ref) That needs to be considered before any surgery or biopsy procedures.
Multiple health issues generally come into play in our pets as they age. Heart valve issues, periodontal disease, digestive tract issues and, liver issues are common in geriatric dogs and cats. They all can exist along side and interplay with kidney issues and it can be quite hard for veterinarians to sort out how much each is contributing to the symptoms you see.
There are many other possible non-kidney causes for the signs and symptoms I just listed. Poor diet, heavy flea or tick infestations, blood parasites, adrenal gland disease and a host of other issues could explain them as well. A thorough veterinary exam and blood and urine tests should be able to sort them out. The simplest is your vet detecting smaller than normal, hard, lumpy kidneys on his/her physical exam. In fat pets, an x-ray or ultrasound might be required to visualize the pet’s kidneys.
In 2013, the Royal Veterinary College in London reviewed their data base on 107,214 dogs treated at British veterinary hospital of a 2-year period. They made some interesting discoveries: Among dogs diagnosed with CKD, those 12 yrs or older had 5.5 times the chance of having CKD than those between 4-7 yrs. Cocker Spaniels and Cavalier King Charles Spaniels had highest increased odds for developing CKD when compared to mutts. The most frequent signs that brought CKD dogs in for their initial examinations were vomiting, increased drinking, urination and incontinence, loss of appetite and loss of weight. Halitosis (periodontal disease ?) vomiting, diarrhea and lethargy were among initial complaints. The median survival time from CKD diagnosis was 226 days (ref)
What Tests Will My Veterinarian Run ?
The most common tests veterinarians use to detect kidney disease are your pet’s blood creatinine and urea nitrogen levels, the specific gravity of your pet’s urine and the presence of albumen in your pet’s urine. After 2016, the SDMA test came into greater use due to the Idexx marketing campaign and a hope that SDMA levels might detect kidney problems at an earlier stage than BUN and creatinine do. Other tests have been discussed, but they are not widely utilized. (ref)
Your Pet’s Blood Creatinine Level
Creatinine is a normal byproduct of your pet’s metabolism - a waste product primarily created by normally functioning muscles (although the meat your pet consumes is also a source of some creatinine). It is not the same thing as the creatine that body builders eat. Vigorous exercise can also cause minor increases in your pet’s blood creatinine levels and dehydration (such as from vomiting or diarrhea) will also raise its creatinine levels. Muscular large dogs also tend to have a bit higher blood creatinine levels. Certain commonly used antibiotics (like Clavamox/Augmentin) and antacids (like famotidine and ranitidine) have been known to elevate blood creatinine levels as well. (ref)
When your pet’s kidneys are functioning properly, they collect creatinine from its blood and deposit it in its urine for elimination. When blood flow through your pet’s kidneys is decreased, or when the kidney’s tiny filters (glomeruli/nephrons) are damaged, creatinine will build up in your pet’s blood stream. I mentioned earlier that a pet’s normal kidneys have a reserve - a backup supply of filtering units. Its only when these reserves have been used up, as in CKD, that blood creatinine levels will begin to rise. A mild-to-moderate elevation in your pet’s creatinine results mean the most when the same pet’s creatinine level has been monitored periodically over several year or when other tests such as urine microalbuminuria or a drop in early morning urine specific gravity (=a more dilute urine) confirm that a kidney issue may be brewing. (ref1, ref2, ref3) The test faces similar issues in cats. (ref) When periodic monitoring consistently determines your pet’s creatinine levels to be in the “high end normal” range (i.e., 1.4 mg/dl for dogs and 1.6 in cats,) , I would still be suspicious that a kidney problem is in its early stages (IRIS Stage 1).
I believe that the sensitivity and significance of the creatinine test could be improved if testing laboratories factored in breed, age, sex and body weight when reporting back if a creatinine test should be considered high, normal or low for a pet. But to the best of my knowledge, national testing laboratories like Antech or Idexx still do not do that. A perceptive veterinary nephrologist recently told me that, in her opinion, the testing lab’s creatinine “normals” were too narrow for large dogs and too wide for small ones. She gave, as an example, that in a Yorkie, a creatinine level of 1.2 mg/dl (=110µmol/L) might be a warning sign of potential kidney issues; whereas a reading of 2 mg/dl (=176.8µmol/L) in a 60-100 pound dog would probably be acceptable.
Many pet owners (and some veterinarians) are under the impression that its the elevation of creatinine and urea (BUN) in pets with CKD that makes pets ill. Actually, they are probably some of the least toxic of the 90 or so known products that build up in the bloodstream when kidneys fail (uremic toxins). (ref) Creatinine and urea are primarily markers for the rest – like smoke is to fire.
Your Pet’s BUN - Blood Urea Nitrogen Level
The amount of urea nitrogen (BUN) present in your pet’s blood can also be an indicator of kidney health. However, it is more subject to changes (fluctuations) that are not due to kidney disease than the blood creatinine test. That is because many other factors can contribute to a rise in BUN (infection, stress, poor appetite, Cushing’s disease, certain medications [eg corticosteroids], liver disease and the degree of kidney BUN reabsorption).
Like creatinine, urea nitrogen comes from the rearrangement and breakdown of protein in your pet’s tissues as well as the protein in your pets diet. Levels of urea nitrogen in the pet’s blood can also fluctuate with a number of conditions such as increased protein intake, intestinal bleeding, infection, fever, dehydration, medications and extensive skin trauma such as burns. Because of that, the blood urea nitrogen test doesn't indicate kidney decline (renal insufficiency) as well as the serum creatinine test. It is still a very valuable test – since two warning alarms are better than one. There are human physicians who still feel that it is a better predictor of approaching mortality in their patients than creatinine. (ref)
Tests To Detect Protein Leaking Into Your Pet’s Urine
Those little filter units, the nephrons, that I mentioned earlier and that are loosing their abilities in CKD contain a very critical group of cells. They are called podocytes. These critters cling to and line the small passages (arterioles) through which blood rushes within the kidney filters. Remember, I mentioned that your pet’s heart send ~ 20-25% of its blood through the kidneys with every beat. Blood is also at one of its highest pressures when it courses through those channels. Podocytes have multiple projections or feet. (feet=podo+cyte=cell). Podocytes arrange themselves to have small slits between these feet (think of them more as fingers). Processes going on within the feet and the small gaps between them normally allow water, salts, and sugars to pass through the slits and out into the urine. When they are healthy, these cells do not allow blood proteins, lipids and blood cells to pass. These cells can vary the size of the slits between them and thus control urine volume as well. They seem to be the ultimate determinants of kidney health. (ref) It is only recently that scientists have become aware of the podocyte’s critical role in kidney health. The details are still being worked out. (ref) No one has figured out a way to regenerate them – but there are folks trying to, and working on other potential treatments. (ref1, ref2, ref3) When they loose their grip on the tiny incoming blood filtering vessels where they belong (the afferent glomerular arteriole capillaries), they wind up in the urine. (ref) One way your veterinarian can get a measure of your pet’s kidney health is by measuring the amount of the pet's blood's protein (mostly albumin) that is slipping by those cells and spilling into its urine. There are other ways protein can get into your pet’s urine. Read about them here.
There are inexact paper dipstick strips - like the ones in the photo above - that will alert your veterinarian that there is protein in a urine specimen. But one cannot rely on their accuracy when they are positive for protein. (ref1, ref2) What they can do is to alert your vet that more sophisticated testing is required. The Urine P:C and the microalbuminuria test are the two tests considerably more accurate in identifying excessive amounts of urine protein. When accessing the source of the leakage, the presence of excessive albumin protein often points to leaking kidney filters.
Your Pet’s Urine Protein to Creatinine Ratio aka UPCR, Urine P:C Ratio
The UPCR test compares the amount of protein found in your pet’s urine to the amount of creatinine found in the urine specimen. That adjusts for the fact that urine can be very dilute or very concentrated at different points in the day and in different situations. Naturally, the more dilute a specimen is, the less protein will be in it and measuring the urine creatinine content adjusts for that. One study in 2005 appeared to show that dogs with higher UPCR ratios tended to live shorter lives than those with lower ratios. (ref) The UPCR test is also the preferred urine protein test choice for many human nephrologists. (rptref) Should you want to delve into this further, here are some additional sources of information: (ref1, ref2, ref3) Although this is a very important test in identifying early cases of CKD in which the blood levels of creatinine and BUN have not yet increased or are borderline, there are other reasons the test might be positive. Fever, heavy exercise, generalized inflammations, blood in the urine, seizures and various forms of stress occasionally caused urine protein and creatinine levels to rise as well. Your vet will sort that out or, perhaps, confirm the results with a second UPCR test. The same caution pertains to the next option, a urine microalbuminuria test. Although there are animal hospitals that run these tests in house, I send them out to a central lab like VCA's Antech or TVMDL. There are also more sophisticated dipsticks (eg Multistix PRO 10LS®) that are can be read in-house on automated strip readers for more accurate results than just eyeballing them (eg Clinitek Status® machine). Although they measure all urine protein, not just albumen, some claim they are just as accurate (ref) I have no experience with them.
The Urine Microalbuminuria Test
Since normal kidneys do not allow much blood albumin to escape into the urine, there are tests that check for its increased presence without comparing it to the amount of creatinine that is present. As with the UPCR test above, non-kidney issues can influence results. Some now refer to this test as an albuminuria test. If I desired this test, I would send it out to a central lab as well. But if one were to run them in a veterinary hospital there are special albumin-specific urine dipsticks, which have a lower detection threshold than standard urine dipsticks. An albumin level above the upper limit is called microalbuminuria or just albuminuria. Cautions on interpretation of the results are the same as the urine protein to creatinine ratio/UPCR test. Some claim that albumin’s presence in elevated amounts in either test will pick up an impending kidney problem earlier than an abnormal blood creatinine test. I do not know if that is true. But when either urine protein test is elevated, a complete urinalysis, blood pressure determination, checking for heart or inflammatory diseases, diabetes, or hyperthyroidism (in cats) etc. are in order for your pet.
The Phosphorus Level In Your Pet’s Blood
There is naturally a lot of phosphorus (in the form of phosphates) in your pet’ body. Next to calcium, it’s the most abundant mineral there. But most of it (~80%) is in the pet’s bones, not its blood. (ref) Phosphorus moves in and out of bone through the blood stream because it is an essential ingredient in all living body cells. (ref) When there is too much phosphorus present in your pet’s blood, it is the kidneys job to excrete it to keep things in balance (homeostasis). Normal kidneys cross-talk with bones in deciding how much phosphorus needs to be excreted into the urine. They do so through a circulating messenger protein produced in the bone, FGF23. FGF23 works in consort with kidney-produced vitamin D and the pet's parathyroid glands – small glands in your pets neck to keep phosphorus and calcium at optimum levels. The phosphorus regulation process begins to break down when too many of your dog or cat’s kidney filtering units, the nephrons, have been lost to CKD. At that point, the phosphorus level in your pet’s blood becomes abnormally high (hyperphosphatemia) and calcium is leached from the animal's bones. Veterinarians believe that high blood phosphorus levels play a significant part in much of the health issues faced by cats and dogs with advanced CKD. Although phosphorus levels occasionally begin to rise even in the early stages of CKD, levels tend to go up in tandem with the other tests I have mentions as the severity of the disease progresses. You can read more about phosphorus problem related to CKD in dogs here and in cats here. Higher serum phosphorus levels are often seen in healthy young, growing puppies and kittens. That is normal.
The Diluteness Of Your Pet’s Urine - Urine Specific Gravity
The refractometer in the photo above is a simple device. It will tell your veterinarian the specific gravity (SG) of your pet’s urine. That is, the percentage of the sample that is pure water in relation to the other elements it contains. The lower the number, the closer the urine is to pure water. The reading varies throughout the day depending on the amount of water your pet consumes or any dehydration it experiences. The first urine of the morning is often the most concentrated and gives your vet an indication of the pet’s maximum kidney urine concentrating ability.
Cats and dogs with progressive kidney disease gradually loose their ability to produce concentrated urine. It no longer has the intense color (and odor) that it once had. To make up for their reduced ability to cleanse their bodies, these pets drink larger amounts of water to take maximum advantage of whatever normal kidney tissue remains. Dogs and cats with health kidneys should be able to produce urine with a specific gravity of at least 1.015 and 1.035 respectively. There are health problems other than kidney disease that can cause your pet to have increased amounts of dilute urine (polyuria) and have excessive thirst (polydipsia). (ref) But persistently low specific gravity urine in a pet is always a cause for concern and an indication that further tests are needed to determine the underlying cause. It is probably unwise to compare the results obtained with one refractometer to results obtained from another. (ref)
In us humans, a moderate decrease in urine specific gravity is considered part of the normal aging process (getting old). By age 40 the average blood flow through our kidneys then decreases by about 10% per decade. In one study, by age 85, roughly half of our glomeruli had lost their urine-concentrating abilities. (ref1, ref2) I do not suppose it is much different in our pets.
Obtaining Your Pet’s Blood Pressure
If veterinarians could get accurate indications of what your dog or cat’s true blood pressure was during its daily activities at home, that information should be extremely helpful in designing an individualized plan to slow CKD. It would also be a boon for evaluating the effectiveness of medications and diet changes as time went by.
There are a few dogs (and even fewer cats) that remain relaxed in a veterinary hospital setting. Although pets may not show it, most are hyper-alert and apprehensive in strange setting. A pet owner’s apprehensiveness and worry is quickly sensed by the dog or cat too. No one has really found a successful way around that – although suggestions abound. (ref1, ref2, ref3, ref4) To a much much lesser extent, it is the same with people – the “white coat effect” . (ref) The second problem is there is considerable disagreement as to what a “normal” blood pressure reading is in dogs and cats really is.
When you go to your doctor, the nurse has a relatively easy time taking your systolic and diastolic (the lower number) blood pressure. Veterinarians rely on only your pet’s systolic blood pressure (the higher number) – machines in common use today in pets can not accurately determine the lower number. Veterinarians and physicians believe that higher than normal blood pressure is damaging to kidneys. That seems intuitively true and many studies have associated increased blood pressure with CKD. (ref1, ref2, ref3) In one study, bringing abnormally high blood pressure down with medications appeared to decrease kidney protein leakage. (ref) A hopeful sign for kidney health.
Physicians and research scientists believe that high blood pressure and CKD is a two way street. Not only does persistent high blood pressure injure the kidneys and hasten CKD; but CKD in itself is capable of causing high blood pressure. (ref) through the release of renin. Whatever the dynamics of CKD in your pet, high blood pressure is an undesirable thing. Only one study I know of did not find an association between elevated blood pressure and the extent of kidney damage (in cats). (ref)
Kidney biopsies (a snippet of tissue taken laparoscopically or surgically) might tell you more about what undesirable processes are occurring in an individual pet’s kidneys. But kidney biopsies are both dangerous and expensive and when the report comes back as “garden variety” glomerulosclerosis, your pet’s treatment options are not enhanced. Kidney biopsies are best reserved for situations where other results do not add up. For instance, an enlarged kidney that might be cancerous. Or kidney failure in a young dog or cat. A biopsy might also be of value to a dog or cat breeder interested in knowing why they have an unusually high incidence of kidney disease in their bloodlines.
The SDMA Test
The SDMA test is the newest test of kidney health available to your veterinarian. In 2018, it is commercially available only through Idexx Laboratories. That is because they patented the test procedure in 2013. (ref) There is little doubt in my mind that SDMA levels rise in pets with kidney disease and there is certainly no harm in running this test. But whether elevated test results are specific only to kidney disease or give your vet more or earlier option to delay the progress of CKD remains highly speculative. By the time you read this article, I may have had time to write an article specifically on the benefits and drawbacks of the SDMA test. I am tracking the results in a number of dogs and cats and would be pleased to add data from your pet as well. The more animals I can match with histories and outcomes, the more accurate the article will be. If have already begun the article, you can read it here.
The National Kidney Foundation is a major advocate for people with CKD. It publishes a journal, the American Journal of Kidney Disease, and has a Guidestar rating of gold (the same as the Boy Scouts). Once I wrote an email to a Tufts nephrologists on the NKF scientific advisory board. I asked why the SDMA test was not recommended as key prognosticator for people with CKD - if it was so desirable in our pets. This was her reply: It is nice to meet you, even if by email. SDMA has some rather weak data as a GFR measurement method in humans. We actually relooked at this data again to see if we should investigate it further and confirmed our interpretation that the data are quite poor. L
A Test That Always Tells The Truth
As a child, I worked for a veterinarian in Brownsville, Texas. Dr. Phillips palpated the kidneys of every dog and cat that came through the door. When one came in with small, hard, kidneys he knew they had kidney issues and told me so. In advanced CKD, the kidneys are firm due to scar tissue and shrunken due to loss of their nephron filtering units. Palpation can be a challenge in overweight pets and those that do not appreciate being poked or touched. Those will need ultrasound imaging or x-rays to detect those changes.
As Time Goes By, What Are The Most Important Things I Need To Monitor In My Pet With CKD ?
Your pet’s body weight is something you can monitor at home. In studies of dogs, cats, underweight pets had significantly shorter survival times once CKD was diagnosed. In some cases (in cats), that weight loss preceded negative changes in their bloodwork. (ref1, ref2, ref3) In humans, obesity has a negative impact on kidney health. So in people, they look at lean muscle mass, not body weight, in monitoring the kidneys because obesity is a known danger for CKD progression. One study found the same trend in dogs. (ref) Commercial “renal diets” tend to substitute fat for protein. So in deciding if they are helpful, you need to be sure it is not just fat that your pet is putting on. But looking back at the outcomes of dogs and cats that had kidney issues that I've seen over the years, I'll take a fat one over a thin one any day.
In advanced cases of CKD, anemia - measured through a simple in-office PCV test - is a quite accurate measure of the advance of CKD. In earlier stages of the disease, checking a drop of early morning urine for its specific gravity is a simple, easily-performed home test as well.
All the other tests I mentioned earlier add data too. But please do not put much faith in meaning of relatively minor fluctuations that occur in any of them. I'm always happier to see them go down or remain relatively flat than when they go up. But tracking them frequently and trying to make too much out of the results leads pet owners (and veterinarians) to needless worry. You are looking for trends.
What Are The Treatment Options For My Cat Or Dog ?
Medications And Diet To Maintain You Dog Or Cat’s Normal Phosphorus Level
High blood phosphorus levels seem destructive to pets with CKD. We have no hard evidence that phosphorus (in the form of phosphate) causes kidney disease in dogs and cats, but as CKD progresses, their blood phosphorus levels tend to go up. (ref) Human physician have similar suspicions. Sugar cane workers in the tropics develop CKD at an abnormally high rate. One theory is that the intense heat in which they work causes recurrent dehydration which injures their kidneys. To compound that, they quench their enormous thirst with high-phosphate soft drinks. (ref1, ref2)
A Diet Change
Initially, a diet change alone might be sufficient to keep your pet’ blood phosphorus levels at normal values. And there is some evidence that in humans at least, the destructiveness of high phosphorus levels begin quite early in kidney disease. (ref) In experimental dogs with induced, kidney failure, limiting phosphorus intake with a low phosphorus diet increased their lifespan. (ref) I plan to write an article about the diet changes you can make for your cat or dog that might slow the progress of CKD. I write when time allows. If I have had the time to write it, you can read it here.
Oral Phosphate Binders
The average humans, diet is thought to contain about 1-3 times the amount of phosphorus the body requires. The average human intake is 1000-1300 mg/day. I do not know what a pet's average intake is, perhaps that data exists. But I believe that cats and dogs can do quite well on considerably less phosphorus than they are probably getting in common diets. As CKD progresses, an intestinal phosphorus binder that lessens the absorption of the phosphorus from your pet’s food is often required in addition to a low phosphorus diet to keep its blood phosphorus level at its lower normal limit. (ref) They work best when given with, just before, or just after a meal. There are a lot of phosphate binders on the market. They all make the phosphorus in your pet’s diet insoluble so that it is not absorbed. It passes out in the pets stools. Some, like Maalox® and Basaljel (aluminum carbonate) contain aluminum and occasionally cause constipation. Although there some concern that ingesting the aluminum they contain might not be a good idea, they are still in common veterinary use. (rptref) Do not give them at the same time you give you pet other medications because they may interfere with the other drug's absorption. Others binders contain calcium carbonate (like Tums®). With those, one must be sure blood calcium levels do not become to high. Products like Epakitin® (Vetquinol) and Pronefra® (Virbac) contain crab and/or shrimp shells in addition to calcium carbonate. Studies on Pronefra® were generated by the makers, Virbac. Naturally, they claim it is the best. (ref1, ref2)
Renalzin®(Lanthanum Carbonate) is another option. It contains no aluminum or calcium. Another advantage of this drug is that it is available as a tasteless liquid. In 2007, the EFSA approved its use (Lantharenol® Bayer) as an additive to be added to an adult cat’s food to decrease intestinal phosphate absorption. (ref) More sophisticated phosphate binders are in use in humans with CKD, resin binders like Sevelamer (Renagel® & Renvela® ) that do not contain calcium or aluminum. You can read what limited data we have in their use in dogs and cats here. Some are known to interfere with the absorption of fat soluble vitamins (like vitamin D/calcitriol). (ref) Pets can dislike the taste of these products. Be sure that their use does not keep you pet from meeting its nutritional needs.
Increased Water Intake And Combating Dehydration
Regardless of what pet food companies would like you to believe, the natural diet of cats and dogs is meat and entrails. Boned animal carcasses are about 70% water, whole rodents, about 66%, dry kibble pet foods about 8%. Most dogs are better about drinking sufficient water to make up for that than cats. But in either species, even mild dehydration can be hard on the kidneys. Sure, feeding dry dog and cat foods is easiest for us. Less time, less hassle, less canned food odor, less halitosis, less cost. But when ar pet faces kidney issues, one ought to consider abandoning dry kibble for a more natural diet. One can also moisten dry pet foods. Begin with just a bit extra water - or , even better, chicken broth and feed multiple smaller meals throughout the day.
One body defense mechanism when faced with CKD, is to pass more water through what functional kidney tissue remains. As I mentioned earlier, that is why pets with CKD tend to drink more. But that can also lead to dehydration if they don't immediately replace that water by drinking. In experimental animals, periodic dehydration and sporadic water intake makes hypertension and kidney damage worse. (ref)
There is also some early evidence that drinking more water slows the progress of CRD in humans as well. (ref)
You can do other things to encourage your pet to drink more: Have multiple water sources for your pet located throughout the house. All pets have their idiosyncrasies. Some drink more from wider shallow bowels that narrow deeper ones. Some prefer bottled water to tap. Some will drink more when their water is flavored – say an added ice cube of meat broth, tuna or clam juice. Some prefer a source of dripping water, others a fountain. Cats often prefer their water sources far from their litter boxes. When pets progress to the later stages of CKD (stage3+) your veterinarian may suggest that that extra fluid be given at home by subcutaneous injection. That is not as extreme as it sounds. Because of their serious kidney issues, these pets are just as susceptible to overhydration from fluids as dehydration. So the fluid must be given slowly and not overzealously. It is also why it is safer to give the fluids under the skin from where they are slowly absorbed rather than intravenously. (rptref) Now giving fluid this way is not the same as peritoneal dialysis. That is a technique in which your veterinarian injects balanced fluids into the space surrounding your pets abdominal organs. After a period of time, the vet will attempt to remove as much of that fluid as possible - hoping that toxin have moved from the blood stream into the fluid.
Boarding CKD pets is unwise. Multiple trips to the vet’s for subcutaneous fluid injections is stressful for cat and owner alike. Most owners learn to master the technique with a little instruction. There are many videos on YouTube that will show you how. Constipation is common in dehydrated debilitated cats that need this therapy. But soupy foods rarely solves the problem without the aid of a mild cat laxative.
Acid Base Balance
The bodies of pets with kidney disease are in danger of becoming too acidic (metabolic acidosis). Normal cell metabolism - the everyday processes that all cells perform - creates hydrogen ions, the source of an acidic body environment. All animals rely on their kidneys to excrete those excess hydrogen ions and to create bicarbonate to keep the body’s acid:base in balance (the pH) within tight limits. (ref) Dogs and cats with kidney problems have problems doing that. In-office blood gas analyzers (eg VetStat, Element POC) can detect the acidity of your pet’s blood. An increased anion gap is also a sign of too much body acidity. When an acid:base imbalance is detected, oral potassium citrate or sodium bicarbonate are the most commonly used alkalinizing agent used to correct it in cats and dogs with CKD. (ref)
Dealing With Poor Appetite
An almost universal occurrence in advanced CKD in cats and dogs is poor appetite. It probably occurs due to a number of things that advanced kidney disease generate. Increased circulating uremic toxins are a likely cause; so are the stomach and intestinal upsets that sometimes occur. Nausea may play a part too. The weakness and apathy of anemia as well. Whatever the causes, they are highly complex. (ref) In humans, it results in a loss of lean muscle mass (protein-energy wasting aka PEW) and it is the strongest predictor of mortality. It is often accompanied by lower than normal blood albumin protein levels (although kidney protein leakage accounts for some of that, poor appetite does as well). (ref) It is the same in our dogs and cats. Studies show that faced with CKD, dogs with the lowest body scores die the soonest (rptref1, rptref2) Thin cats are at increased risk of dying of various other health issues too. (ref)
There are a number of ways you might encourage your dog or cat to eat :
The aroma and texture of canned or freshly-made foods are preferred by most pets over the aroma and texture of dry kibble - have you ever smelled that stuff ? Would you eat it ? Broths, soups and gravies poured over their main diet often encourage pets to eat. So does verbal encouragement and some stroking from their owner. Warmed diets are often preferred over cold ones. Smaller multiple meals may result in daily food intake greater than just two or three. For cats, small amounts of high odor toppings (like sardines or clam juice) may do the trick.
There are also a number of medications vets dispense hoping to improve a pet’s appetite.
Mirtazapine (Remeron®) is sometimes helpful. It is thought to also reduce nausea. Doses in pets with kidney issues may need to be spaced farther apart. (ref)
Some vets or owners have it custom compounded to be given as through the skin (transdermally).
Cyproheptadine, an antihistamine. seems to stimulate some cats to eat. Two AMC veterinarians cover the use of these and other appetite stimulants well. (rptref)
The newest appetite stimulant on the market is capromorelin (Entyce). It is currently only approved for dogs; but it has been given to cats. Read owner experience with this medication here. Your feedback on its effects in your dog or cat is appreciated. When vomiting or nausea interplay with a lack of appetite, mirtazapine sometimes helps but another choice is Maropitant (Cerenia®) – it is best injected chilled. (ref)
Dogs and cats enjoy eating protein. Prescription diets formulated for pets with kidney issues are often less acceptable to a dog or cat than what it was eating before. These diets loose whatever beneficial effects they might have if pets do not eat enough of it to maintain their body weight. You can try several brands to see if your pet prefers one over the other; but I would prefer you prepare a diet from scratch yourself. There are also veterinary nutritional services that will assist you with custom recipes and vitamin/mineral supplements. If I have found the time to write an article on how that is done, you can read it here. Whether dogs and cats with CKD benefit from antacids, other than ones given to bind phosphorus - is controversial.
PUFAs - Polyunsaturated Omega 3 Fatty Acids
Omega 3 fatty acids, the oils mostly extracted from sea creatures, are thought by many to reduce inflammation throughout the body. (ref) Many commercial kidney diets for pets add them as well as antioxidants like vitamin E, C and beta carotene. One early study suggested that PUFAs were beneficial to dogs with experimental kidney failure. (ref) Another contemplated their use in CKD in cats. (ref) A 2012 review of antioxidant use in humans with CKD really couldn’t decide if it was beneficial or not (ref) ; but a study by a group of veterinarians in the Netherlands found that cats fed the commercial diet with the highest PUFA level lived the longest. (ref) So I am inclined to suggest them for your pet with CKD - if given in reasonable amounts. (rptref) Just don’t get carried away. (ref)
Medications To Lower High Blood Pressure
Not all dogs and cats with kidney disease have high blood pressure. But many do and in those dogs and cats, the degree of elevation and the degree of damaging protein leakage into urine seem to go hand in hand in dogs. (ref1, ref2, rptref3) Most veterinarians believe that high blood pressure damages a pet’s kidneys. But it can be a vicious two-way circle. Kidney disease can also be the cause of high blood pressure in dogs and cats (through the renin-angiotensin axis). (ref1, ref2) Giving medications that reduce blood pressure is a first-line treatment for CKD in humans as well. (ref1, ref2)
The two groups of drugs that are in most common use for that are angiotensin receptor blocking medications (ACE inhibitors aka ACE-Is) (ref1, rptref2, ref3) and angiotensin receptor blockers (ARBs such as telmisartan/ Semintra®). (ref) The actions of both relax and widen the diameter of blood vessels (vasodilation) throughout the body enhancing blood flow (decreased vascular resistance) . As blood flow meets less resistance, blood pressure goes down. That same effect is felt in your pet’s kidneys where pressure within the small blood filters (glomeruli) is reduced. They may have other positive benefits. (ref)
Some veterinarians incorporate amlodipine (a calcium channel blocker) - a drug that reduces blood pressure in a different manner - when they feel that ACE-Is alone are not sufficient or when a decrease in the amount of protein leakage into the urine on ACE-1s alone was not what they hoped for. Amlodipine seems particularly effective in cats.
Giving a blood pressure lowing medication to a pet with CKD is not without risk. When it produces a welcome drop in spilled urine protein that is great. But your vet will need to keep careful tabs on the pet’s blood creatinine levels as well. It is not uncommon for these medications to bump up (cause a small rise) in blood creatinine levels. When it is small, that is probably tolerable and the pet may still live longer than it would without the medication. But when it is a significant rise, the pet’s dose of blood pressure medication needs to be lowered, and in some cases, discontinued. It is unclear why this sometimes occurs. Perhaps it was only the abnormally high pressure in your pet’s remaining glomeruli (“super nephrons”) that was holding creatinine levels down. . Perhaps it was due to some other effect that compounds like ACE-Is have. We know these medications affect many systems. (ref) Some consider ARBs the safer option in advanced CKD – at least in humans. (ref)
When these unwanted and unexpected reactions occur, it is more common in the later stages of CKD than the earlier ones. They are also more likely to occur in pets that are dehydrated due to diarrhea, vomiting or the lack of water consumption. One also has to use these drugs cautiously in pets with advanced heart failure. Blood flow (and blood pressure within) their kidneys may already be too low. The same goes for cat with evidence of hyperthyroidism.
Creatinine is only a marker for the many uremic toxins that are thought to rise with it. In pets that don’t tolerate ACE inhibitors or ARBs well, focusing on a low-phosphorus diet might be a safer option. When they are used, your pet’s blood potassium levels need to be followed as well. (ref)
When Should My Veterinarian Start Giving My Pet Medications To Lower Its Blood Pressure ?
Ideally, it would begin when your veterinarian confirmed that your pet’s resting blood pressure had begun to rise above normal. But there are problems here. I mentioned earlier how difficult it is to get accurate blood pressure reading when pets visit animal hospitals. So many vets make the decision based on elevated levels of albumin protein in the pet ‘s urine. The two are assumed to go hand in hand. There really isn’t any evidence that beginning the medications before there is substantial urine protein leakage is of any benefit. (ref)
A small study of dogs that Elanco conducted last year muddied the waters further. They found that a commonly used ACE-I (benazepril) did lower urine protein in dogs. But it did not increase the lifespans of the dogs to which it was given. It also confirmed that benazepril bumps up blood creatinine levels. You can read that study here. As the authors point out, 49 dogs are a small number - perhaps too small to note modest benefits of ACE treatment. But conflicting results are seen across the entire spectrum of CKD field studies in dogs and cats. I think it is much more likely that there are a number of subsets of CKD in our pets as well as pets with multiple coexisting health issues. I believe that is why the results of these studies are so perplexing. Just because we find protein leakage and kidney dysfunction doesn’t mean that the underlying cause and progression is the same in every pet. Until we understand this better, its going to be hit or miss with the drugs, nutrition and lifestyle changes we veterinarians suggest. Some will benefit from one treatment, other from another. Most startling and gratifying to me is that the study was paid for by Elanco, the makers of Fortekor®, the benazepril formula for dogs and cats. There are oodles of glowing reports on the benefit of this and that for pets with CKD. This is the only one I know of where the folks picking up the tab did not get good news. Similar challenges using ACE-Is and ARBs confront physicians treating CKD when their patients have multiple health issues. (ref1, ref2)
Veterinarians are also uncertain as to which dose at which stage of the disease is appropriate. One never wants blood flow through the kidneys to drop so low that the organ is starved of oxygen or remaining nephrons are injured. I would be particularly cautious in pets receiving NSAIDs (eg Rimadyl, Previcox) for arthritis or diuretics (eg Lasix, spironolactone) for heart issues or that are at risk of dehydration or all three (the triple whammy).
Dealing With Anemia
As CKD progresses, it is common for cats and dogs to become anemic. By the time the pet’s packed cell volume (PCV) drops to the low 20s, its energy level, hear and breathing rate will be affected. (stage 3-4). I mentioned earlier that the main cause of this anemia is insufficient kidney production of erythropoietin. At that stage, some veterinarians give their clients the option of opting for erythropoietin or darbepoetin (Aranesp® ) subcutaneous injections – both of which stimulate the formation of red blood cells. Darbepoetin injections have the longer period of action – some times as long as two weeks. Both medications can take 3-4 weeks to show improvement in PVC or RBC numbers numbers. A rather high number of pets have reactions to multiple injections of either product – but less with darbepoetin than erythropoietin. (ref) In an extensive 2017 study, there was no significant differences in the life span of dogs that responded to darbepoetin treatment and those that did not. (ref) Many vets will check these pets for iron deficiency. When present, oral or injectable iron supplementation is desirable.
A blood transfusion is also possible. It is rarely suggested or performed. First, it is expensive. Second, it is quite stressful – the health of a CKD pet is already fragile. Third, there is the possibility of an immune reaction against the transfused blood. Lastly, transfused red blood cells do not tend to last very long in uremic patients.
Are There New Medications In Development That Might Help ?
A lot of pioneering work comes out of the Broad Institute. They are even interested in the genetics of dogs and cats as it relates to the diseases that affect them because they see a better understanding of pet diseases leads to a better understanding of human diseases. One of the interesting compounds they are studying is a TRPC5-inhibitor that seems to have abilities to retard the progress of several forms of CKD. (ref1, ref2) These are early studies in rats. Perhaps something useful will come out of them, perhaps not. (I spoke to the authors about the high incidence of CKD in elderly cats. They were unaware of that).
Another experimental drug combination is LCZ696 (sacubitril/valsartan aka ENTRESTO®) which, it is hoped, might slow the progress of CKD. (ref) There are other compounds under study for a particular form of human kidney disease. They are not the forms of kidney disease commonly seen in dogs and cats, but perhaps there will be cases where they would be helpful:
Sparsentan (RE-021) is one of them. It combines some of the actions of ARBs with those that reduce the effects of endothelins, compounds that also increase blood pressure. If this drug has any potential use in veterinary medicine remains unknown. (ref)
Sulodexide is a compound that might be helpful in reducing protein leakage into the urine (microalbuminuria) in humans whose CKD relates to diabetes. One study found it effective (ref)) the other study did not. (ref) If it has been used in dogs or cats, I am unaware of it.
What About Stem Cell Treatments ?
Colorado State University had a pilot program using feline fat (adipose-derived MSCs) as a source of stem cells (mesenchymal stem cells = adipose-derived MSCs) in hopes that introducing them into cats with renal disease will halt or slow the disease. Their first attempts were in 2009 and clinical trials continued through 2015. In the 2015 report, two out of the four cats were said to have experienced “modest improvement” after intrarenal injection. (ref) In their 2013 study, the stem cells were given intravenously (a lot easier procedure). In those pilot studies, the 16 cats enrolled were said to “not have experienced a clinically relevant improvement”. (ref) I believe the veterinarian conducting those studies has moved on to the vet school at Ohio State University.
There is a lot of interest in regenerative medicine across the span of disease. No one has regenerated kidneys with this technique, but some early data suggests that perhaps the progress of CKD might be slowed. (ref) There is also a lot of hype and quackery across the field. (ref)
Please do keep that in mind when reading glowing testimonials. (ref)
Do Cats Have Some Unique Kidney-Related Risks That Us and Dogs Do Not Generally Have ?
There is a high incidence of hyperthyroidism in older cats. Veterinarians are uncertain why. Hyperthyroidism often leads to high blood pressure - a known risk for kidney disease. In fact, it is very common for feline hyperthyroidism and CRD to exist in the same cat. Hyperthyroidism leads to excessive drinking. That increased water, flushed through the kidneys, masks the CRD until the hyperthyroidism is corrected with drugs or radiation. At that point, some cats go into kidney (renal) failure. So at the least, urine microalbuminuria/UPCR ratios or elevated creatinine/SDMA might inform your vet that thyroid function test (T4) need to be run as well.
How About Kidney Risks That Are More Common In Dogs ?
Elderly dogs are particularly disposed to heart valve issues (generally the mitral valve first). (ref) Once a pet’s heart no longer pumps sufficient blood through the kidneys. Other negative process are probably also in play. (ref1, ref2, ref3) Some veterinarians believe that the reverse may also be the case – dogs with kidney disease may be more likely to develop heart issues. (ref) So a proBNP heart test might be a good choice when kidney tests are abnormal – particularly if your veterinarian detects abnormal heart sounds and/or other evidence of poor circulation.
Arthritis and kidney problems tend to show up about the same time in a dog’s life. Although nothing is proven, one might decide to use NSAIDs cautiously in dogs that show signs of Arthritis and concurrent signs of CKD. It’s a quality of life issue that owners have to decide themselves. There might soon be medications for dogs with arthritis that do not have potential kidney consequences. (ref) No long-term NSID is approved for use in cats. (ref)
What About Hemodialysis Or A Kidney Transplant ?
Long-term hemodialysis is not readily available for dogs or cats. I am not sure why that is, since it is technically possible. When it is performed, it is usually in a university setting being done for one of several causes of sudden kidney injury. Things like antifreeze, grape/raisin poisoning, nibbling on Easter lilies etc. Causes that might resolve in time dialysis give it that time. It is also occasionally used short term when the urine outlets from the kidney (ureters) become plugged (blocked by) with stones or some other obstruction. Standard treatments take 4-6 hours, 2-3 times a week. Long term, it is expensive and a strain on both pet and owner.
There are also veterinary teaching hospitals that perform feline kidney transplants. The University of Pennsylvania School of Veterinary Medicine has the most experience performing them. (ref) The surgical technique, pre and post surgical care vary by institution. (ref1, ref2) PennVet currently claim a 60-70% one-year post-transplant feline survival rate (as opposed to a 97% success rate in humans given human-donor kidneys). I believe that the most common complication, when one occurs, is scarring and inflammation that obstructs the passage of urine from the transplanted kidney (retroperitoneal fibrosis) (ref) Cats with concurrent health issuers or advanced age are poor candidates. I do not know of any programs that currently accept dogs but could be unaware of ones that do. Dogs tend to reject transplanted kidney quite rapidly. They also suffer more infections, blood clots, etc. after the surgery than cats. Kidney transplants are not a cure – the animals must take anti-rejection medications for the rest of their lives (at a cost of about $1,000 per year with periodic testing). The bill for the surgery for one cat at PennVet in 2015 was $16,000, plus airfare, hotels, medical tests and follow-up appointments. With the owners hoping the final bill would not exceed $30,000.
Vets in the UK view the ethics of this procedure differently. (ref)
The 2015 IRIS dog and cat publications recommend considering these procedures for pets in stage 4 kidney failure – as well as of feeding tubes, stomach ports, multiple IVs, peritoneal dialysis and hospice care. (rptref1, rptref2) I cannot imagine a dog or cat wanting to be put through that agony. Your pet loves you. The least you can do for your friend in return at that point in its life is to help send it to Heaven. That, in my opinion, is the only merciful thing to do..