Severely anaemic cats may have very pale gums
Anaemia is defined as reduced numbers of red blood cells (RBCs) in the circulation. Cats are particularly prone to the development of anaemia and hence we often see anaemic feline patients. Feline RBCs have a shorter lifespan (70 days) than many other mammalian species (eg, 110 to 120 days in dogs and humans) meaning that anaemia can develop quite rapidly in cats.
Types of anaemia
Anaemias can usually be broadly divided into regenerative or non-regenerative types (Table 1).
◆ Regenerative anaemias are those in which the bone marrow responds to the anaemia appropriately by producing new RBCs. These can arise as a result of blood loss (haemorrhage) or haemolysis (when RBCs are broken down within the bloodstream).
◆ Non-regenerative anaemias are characterised by the absence of new RBC production in the bone marrow and typically reflect underlying systemic disease or bone marrow abnormalities.
In cats most anaemias are non-regenerative in type.
Additionally multiple causes of anaemia can often be present at the same time in one cat, posing a diagnostic challenge in the investigation of the anaemia, eg, haemolysis caused by Haemoplasma species usually results in a regenerative anaemia, but concurrent feline immunodeficiency virus (FIV) infection can inhibit the RBC regenerative response resulting in a non-regenerative anaemia.
Signs of anaemia
A common sign of anaemia in cats is paleness of the mucous membranes, such as the gums. Cats with severe anaemia can show weakness, an increased heart rate and increased respiratory rate. Anaemic cats may develop pica (a craving for unusual foods) which is typically manifested as licking concrete, eating cat litter or soil. Occasionally cats become jaundiced (yellow discolouration of mucous membranes) with severe acute RBC breakdown (haemolysis). Cats may also show signs of underlying diseases causing anaemia such as chronic renal failure or feline infectious peritonitis (FIP).
Cats which have had a rapid fall in RBC numbers are more likely to show severe clinical signs of anaemia than those cats with a slowly developing chronic anaemia.
Diagnostic testing in anaemia
Examination of blood smears can be very helpful in the diagnosis of anaemia
Anaemia is detected by finding reduced RBC numbers in a blood sample collected from the patient. Anaemic cats have a reduced RBC count, reduced haemoglobin concentration and a reduced packed cell volume (PCV – obtained by spinning a small blood sample in a glass tube and observing the percentage volume taken up by the centrifuged RBCs).
The next step in the investigation of feline anaemia is to determine if the anaemia is regenerative or not. This is done by evaluating the cat’s haematological parameters as well as observation of a stained blood smear. Haematological changes reflecting regeneration include variation in RBC size and the presence of large immature RBCs. The number of reticulocytes (immature RBCs) present in the blood indicates whether active production of RBCs is occurring in the bone marrow, and is used to definitively determine whether an anaemia is regenerative (with lots of reticulocytes) or not (few or no reticulocytes).
As both feline leukaemia virus (FeLV) and FIV can cause anaemia, all anaemic cats should be screened for these viruses. Other tests for infectious diseases may be required, depending on the patient’s clinical signs, such as for feline parvovirus or feline haemoplasma infection (feline infectious anaemia, previously known as Haemobartonella felis). When systemic diseases, such as chronic renal failure, are believed to be the cause of anaemia a thorough investigation of different organ systems is required. This could include biochemical testing on blood and urine samples, radiography, ultrasonography etc. When a bone marrow problem is suspected, collection of bone marrow samples may be required to establish a diagnosis. These samples can be collected from either the forelimb (often the humerus) or hind limb (from the shaft of the femur). A general anaesthetic is required for this procedure in cats.
Treatment of feline anaemia will be partly based upon addressing the underlying cause of the anaemia, eg, antibiotic treatment will be indicated for some infectious causes of anaemia such as feline haemoplasma infection. Cats which are anaemic due to haemorrhage may require supportive treatment for shock. Sometimes the cat’s own immune system is involved in RBC destruction and corticosteroid treatment to suppress an inappropriate immune response may be indicated.
Blood transfusions can be performed on feline patients, and can be a life-saving measure in cats with severe anaemia. However, the existence in cats of naturally-occurring antibodies in the blood that can destroy RBCs from another cat, means that feline blood transfusions must be performed with care. Blood of a matched blood type must always be used. Blood typing can now be performed reliably and quickly in cats using a small blood sample and blood typing cards.
Table 1: Examples of causes of feline anaemia
Can arise due to injury in road traffic accidents, internal bleeding due to tumours, severe parasitism with fleas and lice
(especially in kittens), loss of blood from the gastrointestinal tract or urinary tract because of disease of these systems
◆ Infections, eg, FeLV, feline haemoplasma infection, FIP
◆ Secondary to drugs, tumours, very low blood phosphate concentrations
◆ Heinz body haemolytic anaemia due to oxidative injury to feline RBCs (can be seen with onion poisoning from
feeding baby foods with high onion levels, paracetamol toxicity and disease states such as diabetic ketoacidosis,
hyperthyroidism and lymphoma)
◆ Incompatible blood transfusions
◆ Neonatal isoerythrolysis – can occur when type A kittens are born to type B queens, and they ingest antibodies in the
colostrum that destroy their RBCs resulting in anaemia; this is one cause of fading kittens
◆ Inherited defects (rare) – osmotic fragility (reported in Abyssinians and Somalis), porphyria (in Siamese and DSH, also
causes discolouration of teeth), pyruvate kinase deficiency (in Abyssinians and Somalis)
◆ Primary bone marrow disorders include diseases known as pure red cell aplasia, pancytopenia (which can arise due to FeLV, FIV or
parvovirus infection), abnormal maturation of bone marrow cell lines and leukaemia
◆ Systemic causes of bone marrow suppression such as chronic renal failure (where the kidneys fail to produce
adequate amounts of erythropoietin which stimulates RBC production in the bone marrow), anaemia of chronic disease
(many diseases result in a secondary reduction in RBC production causing a mild anaemia) and FeLV- or FIV-associated
Updated November 2008