Times change and my website needed to change too. To see the 2020 update of this page click this link
To see what normal blood and urine values are for your pet, go here
For an explanation of causes of most abnormal blood and urine tests go here
To see how tests are often grouped, go here
Your pet's free, ionized or available blood calcium can often tell your veterinarian more. Read about that test here
Most of us think about bones and teeth when we think about calcium; but calcium has critical functions in your dog or cat ’s body other than bone strength. Your pet’s bones serve as the storage bank for the important small amount of free circulating calcium in your pet's blood. That blood calcium is critical for many, day to day, life processes that occur within your pet.
Here are some of the important roles of calcium in your pet's body:
Circulating calcium plays an important role in the action of many basic enzymes (enzymatic processes). For example, proteases enzymes that cells require to disassemble proteins into their component amino acids require calcium. (ref) These same enzymes are a necessary part of your pet’s immune system as well. (ref)
Sufficient blood calcium must be present before your pet's blood can clot. (ref)
Circulating calcium also plays a part in keeping your pet's body fluids in their proper place (by contributing to osmotic pressure). (ref)
Calcium is essential for normal muscle contractions. (ref)
When your dog or cat ’s dietary intake of calcium is low, your pet will maintain its blood calcium levels within the proper range even at the expense of its bone strength -- for as long as it possibly can.
A general (entire body) calcium deficiency in your dog or cat is not always due to insufficient calcium in its diet. It can also be because of chronic intestinal or kidney disease, (lack of activated vitamin D (ref) that prevents proper calcium absorption (=Secondary hyperparathyroidism) or because the ratio of calcium to phosphorus in your pet’s diet is not optimal (it should be about 1:1 to 2:1).
None of the symptoms are specific or diagnostic in themselves. In mild cases, you probably would see no symptoms in your pet. When the problem is lower-than-normal blood calcium, you probably would not notice a problem until total calcium levels fell below 6.7 mg/dL.
Veterinarians see more cases of abnormally high blood calcium levels than low blood calcium levels (about 60% of those with abnormal calcium numbers are above normal).
Calcium values can be slightly higher than suggested normal values in immature and growing dogs and cats (particularly the puppies of giant dog breeds).
Higher than normal blood albumin levels have the ability to cause higher blood calcium levels. The most common cause for a higher than normal blood albumin level in pets is dehydration (hemoconcentration, due to lack of water intake, diarrhea or vomiting ). Read more about abnormal blood albumin readings here.
When your pet’s blood albumin level is normal, the most common cause for abnormally high blood calcium level is a tumor (cancer, malignancy) (due to a paraneoplastic syndrome =PNS (ref) ). These are indirect effects of certain types of tumors. The most common ones in dogs are lymphosarcomas and anal sac adenocarcinomas. In cats, lymphomas and squamous cell and bronchogenic carcinomas are the tumors most often responsible. Multiple myelomas (immune system tumors) , thymomas (thymus gland tumors) , osteosarcomas (bone tumors) , and fibrosarcomas also have the potential to raise the blood calcium level of pets.
Chronic kidney disease often cause blood calcium levels in dogs and cats to be abnormally low. But kidney issues in your pet will occasionally cause blood calcium levels to go up - (too high). More pets have calcium levels go down (hypocalcemia) than up (hypercalcemia) . It depends a lot on what portion of the blood calcium your vet is measuring and at what point in the disease process the blood sample was taken.
The calcium in your pet’s blood exists in three forms: part is free ionized calcium , part is bound to blood protein and part is in "complex" with ions (anions) in your pet's blood. In dogs and cats, one can be abnormal while the others remain normal. In cats with chronic kidney disease, about 6% have abnormally high ionized blood calcium while 26% have abnormally low ionized blood calcium levels. By the time these cats are experiencing advanced kidney disease, more than half will have low blood ionized calcium levels despite one in five having high total blood calcium levels (yes, I know it is confusing).
Dogs probably experience the same abnormalities in their chronic kidney disease (CKD). When you know that your pet has kidney disease, measuring its free ionized calcium level is probably the better test to choose (but more expensive and harder to perform).
High blood calcium can be both the cause and the result of kidney disease. Certain rat and mouse poisons contain vitamin D that can damage your pet’s kidneys through excessive calcification (metastatic calcification). Your pet's eating Day Blooming Jasmine can have the same effect. High blood calcium levels have been reported to cause increased urination, perhaps through its ability to interfere with the action of antidiuretic hormone (ADH,AVP, vasopressin) released by your pet’s pituitary gland.
Sudden or Acute Kidney Disease can also be responsible for high blood calcium levels. That can be caused by urinary tract blockage (oxalate or struvite stones, cancer etc.) (ref1, ref2), diseases like leptospirosis, and even grape toxicity). High blood calcium levels can also be found in dogs that consume the artificial sweetener Xylitol (specific ref)
Certain bone infections (osteomyelitis) can liberate calcium, leading to elevated blood calcium levels. Addison’s disease in dogs or acromegaly in cats can also cause high blood calcium levels. High blood calcium levels are also occasionally seen in pets that are infected with some rare fungal diseases (blastomycosis, histoplasmosis, and coccidioidomycosis) and other infections that cause granulomas.
Your pets multiple parathyroid glands, located in its neck (see this illustration), are responsible for regulating the amount of calcium in its blood. Occasionally, one or more of these gland produce its hormone, PTH, in excessive amounts. When seen, keeshonds, labs, German shepherds and cockers top the list of affected breeds. About 40% do not appear ill. In the rest, excessive thirst and urination as well as decreased appetite and activity, shivering and twitching are the most common symptoms. There are theories, but we really do not know the underlying cause of PHPTH.
Cats develop PHPTH too – but even less commonly than dogs. It is even less common in cats than in dogs to ever determine the underlying cause. Some of these cats go on to be diagnosed with cancers (leukemias, osteosarcomas, fibrosarcomas, carcinomas) others with kidney failure – the probable underlying causes.
But in most cats, the underlying cause can never be determined. That is why it is often called Feline “Idiopathic” Hypercalcemia. That is a round-about way of saying “we know what’s wrong but we don’t know why”. Cats with this problem tend to be older (ave age 9 yrs). The most common signs are weight loss (due to anorexia = no appetite) and inactivity (lethargy). Some cats with this problem also vomit or have diarrhea/constipation issues. Many of these cats have a calcium oxalate urinary tract problem as well. Some show abnormal calcification of their kidneys (neprhrocalcinosis). When looking for this condition, measuring your pet's ionized calcium level is more likely to pick up the problem than a total blood calcium level assay is. Idiopathic Hypercalcemia is not the most common cause of high blood calcium levels in cats. Often, it is picked up on a routine health screen without the owners describing a specific health issue in the pet. In one study, only 46% of the cats with high blood calcium had signs of ill health. Some of the cats had mild weight loss, others had IBD, and a few (5% or less) had constipation issues, vomiting or a drop in appetite. Interestingly, 10-15% had urinary tract stones.
Occasional cats seem to benefit from a diet containing lower-than-normal calcium content (about 40% of NRC feline recommendations for Calcium) and restricted amounts of vitamin D3. When the problem is suspected, ionized calcium is the portion of blood calcium most likely to show the elevation. It is possible that a diet low in calcium but high in phosphorus may be a contributing cause. If you home cook , keep that in mind.
High blood calcium levels have been reported in pets that accidentally ate their owners anti-psoriasis medications. (ref) Or that consumed excessive amounts of calcium-containing or vitamin A-containing products. The consumption of excessive vitamin D, either in a vitamin supplement or in rodent poison (Cholecalciferol) can also cause abnormally high blood calcium readings in pets. Lipemic (fatty, non-fasting) blood samples can give falsely high calcium readings. So can accidentally leaving detergent in the blood collection tube or equipment.
As in situations where your pet’s blood calcium levels are abnormally high, situations where they are abnormally low don’t present unique signs. But many dogs and cats with severe hypocalcemia have muscle tremors and twitching. They might walk stiffly, due to cramping, or appear anxious and preoccupied. Others pant, run fevers, (as in eclampsia) or have abnormally fast heart rates. Those with total blood calcium levels below 4.5mg/dL are in danger of dying.
Abnormally low blood albumin protein levels (hypoalbuminemia) are the most common reason laboratory reports come back with low blood calcium levels (probably about half of the lab test reports that report low blood calcium levels are low in albumin as well). Generally the calcium level is not low enough for the dog or cat to show low-calcium symptoms. Your pet’s blood albumin binds to and carries much of the calcium in its blood. When insufficient albumen is present, the total amount of calcium in circulation decreases. In these situations, the pet’s non-bound or free ionized blood calcium generally remains normal.
The two most common causes of serious hypocalcemia are long term (chronic) or sudden (acute) kidney failure or eclampsia.
A major job of your pet’s kidneys is to keep the amount of dissolved blood ingredients at their proper levels. When levels of one ingredient are too high, the kidneys remove the required amount and deposit it in the pet’s urine. When levels are too low, that ingredient is conserved. When kidneys are failing, they loose that ability. One blood ingredient that tends to increase greatly in those situations is phosphorus (blood phosphate). In cases of high blood phosphorus, blood calcium levels inevitably fall. The reason for this is unclear – some suspect that the lost calcium has combined with the phosphorus and been deposited in the pet’s bones. Both long term kidney decline (CRF) or sudden kidney damage can have this effect (hypocalcemia). It may be more pronounced when the kidney damage occurred suddenly and your pet’s body just didn't have enough time to adjust. When the kidney damage is long term (chronic), a condition is called renal secondary hyperparathyroidism is common. It’s seen mostly in dogs, but can occur in cats as well. The high phosphorus levels, due to the kidney damage , causes the pet’s parathyroid glands to secrete excess PTH hormone in an attempt to move calcium from the pet’s bones into its blood stream. The damaged kidneys also fail to produce sufficient active-form vitamin D, which is required to absorb adequate new calcium from foods. The end results are weakened bones. In some dogs, the jawbone (mandible) becomes abnormally flexible as the calcium that gives it its strength is lost (“rubber jaw”).
Sometimes mother pets have problems mobilizing their body’s calcium reserves near the time of birth. The problem is also called pregnancy-related milk fever, parturient paresis or puerperal tetany. It is most common in toy dog breeds, first time litters, or over- supplementation with calcium during pregnancy. The problem is quite rare in cats. The most common signs of eclampsia are tremors and twitching, weakness, agitation, leg stiffness and a reluctance to stand or move. Occasionally seizures also occur.
Despite the fact that this problem responds to giving the pet intravenous calcium along with medications to help lessen their muscle tenseness, blood calcium levels in these pets are more likely to be within the normal range when measured than to be low.
Many human enema preparations (eg fleet enemas) contain phosphate, and , as I mentioned before, anything that makes your pet’s blood phosphate level rise above normal will make its blood calcium level drop.
Acute pancreatic inflammation in pets often causes a mild-to-moderate drop in blood calcium levels. Veterinarians are not certain why, but some think that the release of pancreatic enzyme (lipase) into surrounding tissue plays a part in tying up circulating calcium. A pancreatic hormone called glucagon, that might be released in large amounts during an attack of acute pancreatitis, might also play a role (by stimulating calcitonin release - but If the pet vomits severely enough and becomes dehydrated, blood calcium can actually rise [ref ])
It is the responsibility of your pet’s multiple parathyroid glands to keep the pet’s blood calcium levels adequate. The glands do that by constantly monitoring the pet’s blood calcium level and releasing PTH hormone when levels drop too low. It is quite rare for the parathyroid glands to naturally loose their ability to perform that task. So “natural” hypoparathyroidism is quite rare in pets. Seventeen dogs came into the University of Murdoch Veterinary Clinic with this problem between 1990-2004. Seizures, muscle tremors and twitching, stiff gait, rigidity, muscle cramping, behavioral change and hyperventilation were the most common symptoms. All dogs had abnormally low blood calcium levels and mildly elevated blood albumin levels. (ref)
Your pet’s multiple parathyroid glands are found in its neck. More common than “natural” hypoparathyroidism is accidental (iatrogenic) removal of the parathyroid glands during thyroid gland or neck surgery or due to neck injury or pathology (eg autoimmune disease, tumors etc.) that destroy the glands.
Poorly designed diets, such as those that are primarily unsupplemented red meat or fish fillets are high in phosphorus and low in calcium. (read about that here) Young pets, unfortunate enough to be fed these diets develop rickets. Older pets develop weak bones (osteomalacia). The pet’s parathyroid glands are aware of the situation and attempt to correct it by releasing more PTH. This condition is called Nutritional secondary hyperparathyroidism. Diets that are deficient in vitamin D3 will not allow proper calcium absorption (hypovitaminosis D). Pets fed diets that are deficient in magnesium can also develop hypocalcemia. Intestinal malabsorption/ IBD Digestive tract diseases can prevent your pet from absorbing sufficient calcium from its diet. The same effect can occur when insufficient food is available (starvation) or when your pet is unwilling to eat. You can read about inflammatory bowel disease (IBD) here.
Rhabdomyolysis is a complicated word that essentially means “muscle damage”. When such a situation occurs (such as extreme exertion or subsequent to muscle trauma), injured muscle cells release a lot of phosphate. I mentioned that as phosphate goes up, blood calcium goes down. That, plus the kidney damage that often accompanies severe muscle damage, is thought to be the reason the pet’s blood calcium levels fall.
Ethylene glycol poisoning causes large amounts of oxalate to be produced in your pet’s body. That oxalate binds to circulating blood calcium to form calcium oxalate. So blood calcium levels fall. The kidney damage that often occurs after that aggravates the situation as it often has the same blood calcium lowering effect as any form of sudden kidney destruction. Antifreeze is not the only product that can cause oxalate poisoning leading to hypocalcemia. Certain plants (including lilies and, philodendron) can contain large amounts of oxalate. (ref)Certain Specific Cancers
Medullary carcinoma of the thyroid gland and primary (began there) and metastatic (moved there) bone tumors have been associated with hypocalcemia.
Accidental use of blood collection tubes that contained EDTA, citrate or oxalate anticoagulants will give falsely-low blood calcium readings. Pets that receive substantial blood transfusions containing citrate anticoagulant can also have low blood calcium readings because the citrate ties up their blood calcium. Pets that in emergencies receive large amounts of IV fluids that have no calcium added to them can simply dilute the amount of calcium in the pet's blood stream. Pets that receive intravenous phosphate to correct abnormally high blood calcium levels sometimes subsequently dip too low in blood calcium. Therapeutic doses of sodium bicarbonate (NaHCO3), used to correct metabolic acidosis can have the same effect (ref)
CBC and blood chemistry panel, more specifically, run blood phosphorus, glucose, BUN, Creatinine [kidney function], potassium, urinalysis, ionized calcium,, EKG , PTH levels for parathyroid gland function, Parathyroid hormone related protein (PTHrP) test for evidence of cancer, Review of diet and nutrition, Note if hypocalcemic tetany improves with IV calcium. Body temperature for fever, amylase, and pancreas-specific lipase (when pancreatitis is suspected) T4 for hyper or hypothyroidism, , ACTH stimulation test (to access adrenal gland function wen required), [This diagnostic flowchart for low blood calcium might be helpful as well]