Anaemia in cats

Everyone knows that humans can get anaemia for one reason or the other, but did you know that anaemia is as common a health problem in cats?

Feline anaemia is a problem for cats because the condition means that there are fewer red blood cells in the cat's system. Because red blood cells (RBC) carry oxygen from the lungs to different parts of the body, a cat with anaemia suffers from oxygen deficiency. So an anaemic cat is weak, lethargic and may lose her appetite. Anaemia in a cat can be a serious health problem, not least because the anaemia is generally itself a symptom of an underlying medical condition.

There are two main types of anaemia in cats: regenerative and non-regenerative. With regenerative anaemia, the bone marrow (the tissue inside the bones which produces blood cells) can still produce new red blood cells when it gets the signal from the body to do so. Regenerative anaemia can happen in various circumstances such as sudden blood loss due to injury or damage to red blood cells - for example during a viral infection. In regenerative anaemia the cat's body works hard to replace vital blood cells. Whether it succeeds depends on the extent of the blood cell loss and the efficiency with which the regeneration takes place.

Non-regenerative anaemia is when the bone marrow can't produce new blood cells. In cats the most common reason for non-regenerative anaemia is chronic renal failure (CRF) - an incurable progressive disease. The anaemia happens because the degenerating kidneys are unable to keep producing a hormone known as erythropoietin (EPO) which stimulates the bone marrow to produce more RBC. Red blood cells in the body last for around 100-120 days so the body has to continually keep replacing these cells as they wear out.

In anemic cats with healthy kidneys, the kidneys actually increase the EPO production to alert the bone marrow to step up red blood cell production. In CRF cats, as the kidneys become more damaged the amount of EPO in the system goes down. The bone marrow no longer receives the signal to produce RBC and this eventually leads to anaemia.

Diagnosing anaemia

Possibly the most visible symptom of anaemia in a cat is the loss of the normal pink color of the cat's gums. If your cat's gums seem unnaturally pale, or if red blood does not flow back under the skin once the gums have been lightly pressed with a finger, make sure that your cat is seen by the vet as soon as possible.

The only way to confirm anaemia in cats is with a blood test. The total number of red blood cells per millilitre of blood will tell the vet if the cat is anaemic, and how severe the problem is. The vet will also count immature red blood cells (these are called reticulocytes. Though immature, reticulocytes can still carry oxygen.) A reticulocyte count helps to diagnose the type of anaemia. A small number of reticulocytes are always present in the circulation, but the number is small because most RBC emerge from the bone marrow as fully mature cells. If a cat has more than the normal level of reticulocytes that suggests that the bone marrow has recognised a need for new RBC and is pumping them out as fast as they can be produced. An increased number of reticulocytes also tells the vet that the bone marrow is working, so the anaemia is likely to be regenerative.

If the number of reticulocytes is lower than normal then new blood cells are not being produced, which suggests non-regenerative anaemia.

What causes anaemia?

Feline anaemia is not a primary disease. That is, a cat becomes anaemic because something else is wrong. CRF (chronic renal failure) is often the culprit, but there are many other possible causes. These can be something as simple as fleas or another parasitic infection which feeds on cat blood. There may severe blood loss due to trauma, a bleeding ulcer or a tumor hijacking the body’s blood supply. There are also pathogens which destroy red blood cells, such as the feline leukemia virus or feline immunodeficiency virus.

Many cats can develop anaemia after ingesting toxins - even something as benign as an aspirin can cause problems in a system for which the medication is not designed. The moral here is that what is medicine for humans can be poison to a cat - and the other way around.

With cats (and humans) a poor diet can lead to a deficiency in certain B vitamins, particularly vitamins B12 and B9 (Folic Acid), and this can cause non-regenerative anaemia among other problems.


If the anaemia is regenerative, and the bone marrow is doing a good job, there is no need to do anything about the anaemia. The important thing is to establish the underlying cause of the anaemia and deal with that. Once the blood cell loss has been dealt with the anaemia should clear up. If the RBC count is very low a blood transfusion might be needed to stabilize the cat while the original disease is treated.

In a case of non-regenerative anaemia, especially in cats with CRF, the administration of a form of the hormone EPO is helpful about 70% of cases. The EPO used to tell bone marrow to start red blood cell production can be either human or feline. However for some reason 30% of cats treated with EPO develop antibodies which neutralize the hormone before it can get the bone marrow working. To make matters worse these antibodies go on to neutralize whatever EPO the cat's own kidneys are still producing. This results in the blood cell count rapidly plunging to life-threatening levels for which a blood transfusion is the only treatment. Scientists are still trying to find out what causes some cats to produce anti-EPO antibodies, but it may be a while before they solve the problem.

Note: This information is for guidance only. It is not intended to replace consultation with a licensed practitioner.

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