What Is Anaemia in Cats?
Anaemia is a reduction in the number of circulating red blood cells or the amount of haemoglobin they carry. Red blood cells are responsible for transporting oxygen from the lungs to every tissue in the body, so when their numbers fall, cells throughout the body receive less oxygen than they need.
Vets measure anaemia using the packed cell volume (PCV), also called the haematocrit. This is expressed as a percentage of the blood volume occupied by red blood cells. In healthy cats, the PCV is typically between 30 and 45 per cent. A PCV below 25 per cent is the threshold at which anaemia is considered clinically significant. Severe anaemia — a PCV below 15 per cent — is a medical emergency.
Recognising Anaemia in Your Cat
The signs of anaemia reflect the body's struggle to deliver enough oxygen:
- Lethargy and reduced interest in activity
- Pale, white, or grey gums (normally gums should be salmon pink)
- Rapid or laboured breathing, even at rest
- Weakness, difficulty jumping, or reluctance to move
- Loss of appetite
- Elevated heart rate
- Collapse in severe cases
Pale gums are one of the most reliable quick checks an owner can perform at home. Press a finger against your cat's gum, release, and the colour should return within two seconds. Gums that are white, very pale pink, or yellowish require urgent veterinary attention.
Types of Anaemia: Regenerative vs Non-Regenerative
Classifying anaemia as either regenerative or non-regenerative is one of the most important steps in finding its cause.
Regenerative Anaemia
In regenerative anaemia, the bone marrow is responding normally to the loss of red blood cells by producing new ones at an accelerated rate. Immature red blood cells called reticulocytes flood into the bloodstream and can be detected on a blood smear or specialist reticulocyte count. The two main causes of regenerative anaemia are:
- Blood loss — from trauma, internal bleeding, parasites such as fleas or ticks, or gastrointestinal ulcers
- Haemolysis — premature destruction of red blood cells, which may be caused by immune-mediated haemolytic anaemia (IMHA), infections, toxins, or parasites such as Mycoplasma haemofelis
Non-Regenerative Anaemia
In non-regenerative anaemia, the bone marrow is failing to produce enough red blood cells. Reticulocyte counts are low or absent. Causes include:
- Chronic kidney disease (CKD) — the most common cause in older cats
- Chronic inflammatory or infectious disease
- Bone marrow disorders including leukaemia or aplastic anaemia
- Nutritional deficiencies
- FeLV (feline leukaemia virus) infection, which directly suppresses the bone marrow
The Role of FeLV and FIV Testing
Testing for feline leukaemia virus (FeLV) and feline immunodeficiency virus (FIV) is essential in any anaemic cat that has not already been screened. Both retroviruses significantly impact the immune system and bone marrow.
FeLV in particular is strongly associated with anaemia. It can suppress red blood cell production directly, cause immune-mediated destruction of red blood cells, or predispose affected cats to bone marrow cancers. FIV tends to cause a more chronic immunosuppression that makes cats susceptible to secondary infections, some of which can trigger anaemia.
These tests are simple in-clinic blood tests that produce results within minutes. They should be performed in any unvaccinated cat, any cat with outdoor access, or any cat whose status is unknown.
Immune-Mediated Haemolytic Anaemia in Cats
Immune-mediated haemolytic anaemia (IMHA) occurs when the immune system mistakenly targets and destroys the cat's own red blood cells. In dogs, primary (idiopathic) IMHA is common. In cats, it is far less frequent, and secondary IMHA — triggered by an underlying cause such as Mycoplasma haemofelis infection, FeLV, certain drugs, or other diseases — is more typical.
Diagnosis involves the Coombs test (which detects antibodies on red blood cell surfaces), blood smear evaluation, and investigation of underlying triggers. Treatment targets both the immune response — using steroids or other immunosuppressants — and any identifiable underlying disease. Doxycycline is the antibiotic of choice if Mycoplasma haemofelis is identified or suspected.
Anaemia and Chronic Kidney Disease
CKD is extremely common in middle-aged and older cats, and anaemia is one of its most significant complications. Healthy kidneys produce a hormone called erythropoietin (EPO) that signals the bone marrow to produce red blood cells. As the kidneys fail, EPO production falls, and the bone marrow slows its output accordingly.
This EPO-deficiency anaemia was historically treated with human recombinant EPO, but this frequently triggered an immune reaction in cats that destroyed the injected EPO and the cat's own EPO simultaneously — worsening the anaemia permanently.
Darbepoetin alfa is now the preferred treatment. This synthetic EPO analogue, originally developed for use in human dialysis patients, is far less likely to trigger an immune response in cats. It is given by subcutaneous injection, typically once weekly at first, then at longer intervals once the PCV has stabilised. Response rates are good, and many cats show significant improvement in energy and quality of life within weeks. Iron supplementation is often given alongside darbepoetin, as iron stores are rapidly depleted when the bone marrow is stimulated to produce more red blood cells.
Blood Transfusions in Cats
In severe or rapidly progressing anaemia, a blood transfusion may be required to stabilise a cat while the underlying cause is treated. This is a more complex undertaking in cats than in dogs, for one critical reason: cats have blood types.
The feline blood typing system has three groups: A, B, and AB. Type A is by far the most common. Type B is less common but occurs more frequently in certain breeds, including British Shorthairs, Birmans, Persians, and Ragdolls. Type AB is rare.
Cats with type B blood have naturally occurring strong antibodies against type A blood. If a type B cat receives type A blood — even in a small first transfusion — a life-threatening transfusion reaction can occur almost immediately. Blood typing of both donor and recipient before every transfusion is therefore mandatory. Cross-matching is also recommended to check compatibility at a cellular level.
Typed feline blood donors are maintained at some referral centres and veterinary blood banks. Emergency transfusions require planning; owners of cats with type B blood and known anaemia risk should discuss this with their vet in advance.
When to Seek Urgent Help
Any cat with very pale or white gums, rapid breathing at rest, sudden collapse, or profound weakness requires emergency veterinary care. Anaemia can deteriorate rapidly, particularly in cases of acute blood loss or haemolysis. Early diagnosis, blood typing, and targeted treatment significantly improve outcomes across all types of feline anaemia.