Causes Of Anemia In Dogs And Cats

Ron Hines DVM PhD

When your pet is anemic, rapid breathing, weakness and pale gums are what you will probably notice first. But your veterinarian’s stethoscope might also detect a fast pulse and heart murmur in anemic pets.

Anemia is the presence of too few red blood cells circulating in your pets body.

Your Pet’s blood is composed of a liquid portion, the plasma, and a cellular portion. That cellular portion is made up of red blood cells (=erythrocytes =RBCs) which carry oxygen throughout its body, platelets (thrombocytes) that allow its blood to clot when it is necessary and white blood cells (leukocytes), which are responsible for fighting disease. In most anemic pets, an underlying disease is interfering with the complex processes that allows red blood cells to form within your pet’s bone marrow. That blood-forming process is called erythropoesis.

There are two basic kinds of anemia. In the first kind, the pet’s body loses blood faster than it can be regenerated but the animal is still able to produce new red blood cells (RBCs) in its bone marrow. This is called regenerative anemia. In the second form, the pet has lost its ability to manufacture new RBCs in its bone marrow. This type is called non-regenerative (once called aplastic anemia). (ref) A mark of a regenerative anemia is that the body is in a rush and releases some of its RBCs a bit too early. Those young RBCs are called reticulocytes. An increase in their number might help your veterinarian to decide which form of anemia is affecting your pet. Regenerative anemias are sometimes called blood-loss anemias. You can read more about regenerative anemias here.

What Signs Might I See If My Pet Is Anemic?

Anemic dogs and cats must  breath faster  to keep their bodies oxygenated. Their hearts will also beat faster in an attempt to keep their body better oxygenated. These pets usually have low energy levels.

You might notice that your pet’s gums or the shiny pink mucous membranes of its eyes (sclera) and skin of its nose and ears are paler than they should be. Anemic animals often become weak and lethargic (“mopey” or sluggish ). They might sleep more than usual and their toes and ears might be cooler than normal. They might not groom themselves as carefully as they used to. They might loose their normal interest in food and play-time and they usually pant and rest after minor exertions that never bothered them before.

Because animals with anemia have fewer red blood cells, their blood is thinner (more watery). As a result, anemic animals often develop heart murmurs that your veterinarian might hear through a stethoscope. The noise a heart murmur makes comes from the turbulent sound thinner blood makes as it flows through the valves of your pet’s heart.

The signs of anemia depend on its severity and how quickly the anemia occurred. With gradual onset of anemia, the pet’s body has time to adjust as best it can to its decreased red blood cell count. Animals that become anemic very quickly may die because their bodies just cannot handle the sudden loss in red blood cells and oxygen.

How Will My Veterinarian Determine If My Pet is Anemic?


When your veterinarian suspects that your pet is anemic, the vet will perform a simple blood test in the office that determines the volume (percentage) of erythrocytes present in your pet’s bloodstream. This test for anemia is called a “packed cell volume” or “hematocrit” (= PCV, Hct). A drop of blood is introduced into a thin glass tube and spun in a centrifuge to separate the red blood cells from the blood serum or plasma. The shorter the column of red cells, the more anemic the pet is. Your veterinarian may also stain and examine a thin film of your pet’s blood on a slide to determine the characteristics of the red cells and blood platelets that are present. In this way, your vet can often see clues that distinguish between regenerative and non-regenerative anemias. You can read about how central veterinary laboratories work with your local veterinarian to determine the cause of canine anemia here ; and in cats here. The search for clues as to the cause would be similar in ferrets as well. The shape (morphology) size and color of individual red blood cells in your pet’s blood are all important clues. You can read more about some of those clues here.

Regenerative Anemias

Regenerative anemias are those in which the pet’s body is producing new red blood cells to replace those that were lost. That implies that blood is leaking from its circulation or body somewhere or pooling in an organ such as the spleen (one cause of splenomegaly) and that your pet still has the capacity to produce new red blood cell replacements. Sometimes, the cause is a sudden major blood loss – like that occurring after a large wound or accident. At other times, it is a slow and steady blood loss – like that which accompanies stomach or intestinal ulcers. In other cases, regenerative anemias are due to heavy burdens of intestinal parasites such as hookworms. Many of these regenerative anemia cases have a better outcome than non-regenerative anemias in which the pet’s body is no longer able to produce new red blood cells because of an underlying health problem. Veterinarians almost always run blood serum analyses (blood chemistries) and a white blood cell counts on anemic animals to help them determine the cause of the problem.

Blood Loss Anemia

Cats that are persistently anemic with no ready explanation should have a PCR test run on their blood for evidence of hemotropic mycoplasma. (Antech T985 Fast Panel PCR-FHMP or Idexx RealPCR™ ). It is carried by fleas. Not all positive cats are anemic when they have these organisms nor The most common cause of regenerative anemia in young pets are intestinal parasites (e.g. hookworms). You can read more about those parasites through this link. Another common cause of anemia in young pets is heavy flea infestation. Although each flea only sucks a minute amount of blood the combined loss of blood in immature animals can be great. You can read about the health problems that fleas cause in pets through  this link . Hemoglobin, the red pigment of blood, contains iron. In both instances so much iron is lost from the body that the red blood cells subsequently produced are smaller than normal (microcytic anemia).

The most common cause of blood-loss anemia in adult dogs,cats and ferrets is traumatic blood loss due to a large wound. In older pets these blood-loosing “wounds” are often the result of bleeding cancers in the walls of the pet’s gastrointestinal tract or urinary system.

Another cause of blood loss – especially in dogs – is the administration of non-steroidal anti-inflammatory medications including aspirin, ibuprofen, phenylbutazone and naproxen and pyroxicam. These medications can cause bleeding ulcers of the stomach and small intestine leading to anemia. These type of drugs are often given to dogs that suffer from arthritis. You can read about those medications and their possible side effects through this link.

In ferrets, sudden bleeding into the intestinal tract (acute hemorrhagic gastroenteritis) is the most common form of sudden blood loss. It can occur slowly as well when ferrets suffer from inflammatory bowel disease (IBD). Occasionally, anemia in ferrets is due to the ingestion of sharp foreign objects. More commonly, it is the result of stress or bacterial intestinal infections (campylobactersalmonella) when under cooked or raw meat products are included in their diets. None of these causes are as common as the non-regenerative anemias associated with prolonged heat periods in unspayed female ferrets. You can read about that here.

Some pets become anemic because their blood does not clot normally. Read about many of the health issues responsible for that the organism necessarily the cause of their anemia; so a coombs test might also be indicated.

How Can My  Veterinarian Treat My Pet’s Anemia?

Mild to moderate cases of anemia are treated with blood-building vitamins and minerals called hematinics and treatment of the underlying cause. Severe cases of anemia often require transfusions. Luckily, severe transfusion reactions seem to be less common in pets than in human beings. Anemia never occurs without an underlying deficiency, disease or accident. So correcting anemia without correcting its underlying cause is never a permanent cure for your pets problem. Anemias that occur in animals less than half-way through their natural lifespan often respond well to treatment when the underlying cause is identified and corrected. Often, anemias that occur in older pets do not have as favorable an outcome. Mild to moderate anemia, in itself, is not a painful or distressing condition – its chief symptom is a lack of energy. So in older anemic pets, lifestyle changes, nutritional support and keeping underlying or coexisting health problems at bay is often enough to keep the pets happy.

What is Red Blood Cell Hemolysis?

Hemolysis is the sudden destruction of red blood cells within the veins and arteries of the body. This can be caused by the ingestion of toxic materials, bacterial and viral infections, defectively produced red blood cells, autoimmune disease and parasites of the blood (Haemobartonella [the old name for hemotrophic mycoplasma] and babesia). These are sometimes sudden crisis events. Transfusions alone are not effective in treating hemolysis because the new blood is destroyed as quickly as it is added. Many cases of hemolytic anemia in pets are treated with antibiotics and drugs that slow the destruction of red blood cells (corticosteroids). The gums and white portions of the eyes of animals with hemolytic anemia are often yellowish ( icteric  ) due to the presence of an excess of destroyed hemoglobin products within the body (bilirubin).

Both Tylenol® (acetaminophen/paracetamol) and onions can cause anemia in cats.

Accidental eating of zinc-based coinage (US pennies) will cause anemia in all species of animals. An auto-immune disease (autoimmune hemolytic anemia) is a common cause of hemolysis in older adult pets, particularly dogs.

Non-regenerative Anemias

Some time ago, the most common cause of non-regenerative anemias in female dogs was the administration of estrogens. This was commonly done to end unwanted pregnancies. A similar estrogen problem (sertoli cell tumor ) occasionally occurs in male dogs that have undescended testicles (cryptorchids ). You can read about that problem here.

The most common cause of anemia in cats is infection with the feline immunodeficiency or feline leukemia virus .

The most common cause of non-regenerative anemia in ferrets is elevated blood estrogen levels in unspayed female ferrets undergoing prolonged heat periods (estrus or breeding cycles). Non-regenerative anemia is also sometimes seen in the leukemias and adrenal cell tumors common in pet ferrets. You can read more about the more common causes of anemia in ferrets through this ink.

In non-regenerative anemias it may be necessary to examine samples of the blood-forming marrow of the bones to determine the cause. This procedure is called a bone marrow biopsy. You can read about that procedure here.

The Feline Leukemia Virus

Often, the first signs of Feline leukemia (FLV) in cats are unexplained chronic low-grade fevers and anemia. These anemias are due to the effects of the FLV on the blood forming elements within your cat’s bone marrow. You can read more about feline leukemia through this link.

The Feline Immunodeficiency Virus

As with FLV, feline immunodeficiency virus (FIV) often causes anemia in cats through its effect on bone marrow. Complicating matters, cats with FIV often have poor appetites and will not eat a balanced diet. Diets low in iron, and vitamin B-12 can exacerbate these anemias. Cats with FIV or FLV may also have decreased resistance to the blood parasites that often cause anemia in themselves. You can read more about feline immunodeficiency virus through this link , about one of those parasites, haemobartonella (Mycoplasma haemophilus), here and the other, ehrlichia, here.

Fight Abscesses In Cats

Indoor/outdoor cats that fight, as well as unneutered stray tomcats are very susceptible to septicemias (bacteria in the blood stream) and subcutaneous abscesses. These often result in toxic, non-regenerative anemias early in the condition. Once the infections coalesce into an abscess and begin to drain, the anemia almost always subsides unless the pets are already positive for FLV, FIV or both of these virus.


Many forms of cancer liberate products into the bloodstream that suppress the formation of red blood cells in the bone marrow. Generally, cancers that cause anemia are the more life-threatening forms of cancer. Small, benign tumors do not cause anemia. In certain types of cancer, erythropoietin production by the kidneys, as well as its activity on the bone marrow, is inhibited by cancer-produced cytokines (the substances that mediate inflammation) as well as by chemotherapeutic drugs drugs. You can read more about cancer in pets through this this link.

Anemia Due To Kidney Failure

Kidney failure in animals leads to a buildup of toxic waste in the blood stream that suppresses blood cell formation (uremia ). In chronic renal failure, the pet’s kidneys cease to produce sufficient amounts of a hormone, erythropoietin, necessary for blood cell formation in the bone marrow. Human erythropoietin has been available since 1989. However, it has not worked as well as we had hoped in animals because each animal species’ erythropoietin is slightly different from the other. Most cats eventually build up immunity to human erythropoietin. Perhaps, the lives of cats suffering from non-regenerative anemia might be improved by administering synthetic (recombinant) feline erythropoietin (rfEPO) developed at Cornell Veterinary School. (ref) There have also been a few studies on treating this problem in cats with gene therapy (ref). Studies on the use of canine erythropoietin were also underway at that School (ref). But since there has been a 10-year lapse in publications and announcements about those therapies, they must not have turned out to be as promising as initially hoped. You can read more about kidney failure in cats through this link and in dogs here and here.  

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