Why Is My Dog's Reticulocyte Count Abnormal ?
Why Is My Cat's Reticulocyte Count Abnormal ?
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
Ron Hines DVM PhD
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Your Pet's Reticulocyte Count
Reticulocytes are your pet’s youngest red blood cells (RBCs). They are slightly larger than its older, more mature, red blood cells (erythrocytes) that make up most of the red cells in its blood.
Reticulocytes retain a bit of lacy material that was once part of the protein-making factories (ribosomes) of the bone marrow cell from which it originated. After a few days in your dog or cat’s circulation, that material disappears and reticulocyte becomes an ordinary red blood cells. Although not exactly describing the same thing, increased reticulocyte numbers and polychromasia generally go hand in hand (occur together).
If your dog or cat becomes anemic and its bone marrow is healthy, the number of reticulocytes in its blood will rise. When reticulocyte counts do not rise in your anemic pet, veterinarians call the situation an unresponsive (aplastic) anemia. The cause is usually located in your dog or cat’s bone marrow where these cells form.
When your veterinarian considers the importance of your pet’s reticulocyte count, he/she must do so knowing your pet’s packed cell volume (PCV, Hct). That shouldn't’t be a problem because a reticulocyte count is usually a standard part of the CBC / WBC test panel that the vet ordered to be run on the blood sample taken from your cat or dog.
Because the blood of anemic pets is more dilute. There will be less reticulocytes per volume of blood than in non-anemic animals. That would falsely lower your pet’s reticulocyte count. To get around that, a reticulocyte index (RI) value can be obtained to adjust for any anemia that is present.
Reasons Why Your Dog Or Cat ’s Reticulocyte Count Could Be High (Reticulocytosis) :
The usual cause is lack of enough working red blood cells = anemia.
When your cat or dog becomes anemia for any reason, its entire body, including its kidneys are starved for oxygen. That low oxygen situation causes normal kidneys to produce a hormone called erythropoietin, which encourages the pet’s bone marrow to increase its production of new red blood cells. In the process, there will be more of the younger reticulocyte RBCs released into your pet’s blood stream.
So anemia from any cause should cause an increase in your pet’s reticulocyte count. Rather than list all of those causes again, find them listed for the reason your pet’ PCV or hemoglobin might be low. In kittens and puppies, heavy flea infestations are a common cause.
Intravascular (within the blood vessels) red blood cell destruction (hemolysis) can also increase your pet's reticulocyte count. When an event like that occurs, it is usually due to an auto-immune diseases in which the pet's own antibodies are mistakenly directed against its own red blood cells. Onion ingestion can cause it as well - as can a mismatched blood transfusion.
There are mixed feelings as to whether cats that eat bentonite-containing cat litter are predisposed (more susceptible) to anemia with an associated elevation in their reticulocyte counts. Only a few poorly-verified cases have been reported.
What If My Pet Has A High Reticulocyte Count But Is Not Anemic ?
An elevated (high) reticulocyte count can persist for a while after a pet has overcome a period of anemia - say after having bled severely due to a car accident. Higher than normal reticulocyte counts in the absence of anemia were also found to occur more frequently in dogs taking NSAIDs medications like carprofen (Rimadyl®) or meloxicam to treat their arthritis or other chronic pain conditions. Veterinarians suspect that chronic stomach and/or intestinal bleeding caused by these medications is the cause - but any cause of chronic bleeding - seen or unseen - or extreme exertion can have this same effect. (ref1, ref2)
Reasons Why Your Dog Or Cat ’s Reticulocyte Count Could Be Low :
Lag time. Anemias due to sudden blood loss when your pet’s bone marrow has not had time to increase its RBC production can have low blood reticulocyte numbers. It takes 2-4 days from the time of blood loss for your pet's reticulocyte numbers to climb.
Blood loss over extended periods of time, such as intestinal bleeding from parasites or a tumor, can deplete your pet’s iron reserves; eventually turn a high-reticulocyte-count, responsive anemia into a low-reticulocyte-count unresponsive anemia. That is because your pet’s bone marrow might eventually runs out of iron to use in new RBC formation. That is why giving an appropriate amount of an iron supplement is a wise move after severe bleeding. The same problem can occur in chronic intestinal inflammation such as IBD when folate and vitamin B12 as well as iron are depleted.
Non-regenerative (aplastic) anemias can occur in cats and dogs when tumors or pre-tumorous cells replace or crowd out normal bone marrow cells.
Similar non-regenerative anemias with low reticulocyte counts often occur due to cytokine chemicals released in the advanced stages of large number of chronic inflammations and cancers. Many have nothing directly to do with your pet's red blood cell generation process. It is very unusual to find end-of-life pets that do not have some degree of non-regenerative, low-reticulocyte anima of this kind.
I have found that pets in this situation seem to know that their life is ending. They are calm, loving and not fearful. The best thing to do for them at that stage is spoil them with love and whatever they might be willing to consume in the way of fluids and nutrition. "Heroic" veterinary intervention at that point is not in your pet's interest.
Low-reticulocyte anemias are a big problem in advanced feline leukemia (FLV). It can also occur in panleukopenia virus infection or associated with ehrlichia infection .
A non regenerative, low-reticulocyte anemia, can also occur when pets have consumed lead-containing objects. Methimazole, used to treat hyperthyroid cats has caused aplastic, low-reticulocyte anemia in humans. It is unclear if that can be a side effect in cats as well. Various medications given to dogs and cats for the treatment of cancer for their tumor-cell-destroying properties can damage the pet’s blood forming bone marrow as well. That is why the CBC/WBC of pets receiving those medications needs to be closely monitored.
Complementary Tests :
When reticulocyte counts are high, tests to determine why and where blood loss is occurring.