Anaemia is the term used to describe reduced numbers of red blood cells (RBCs or erythrocytes) in the circulation.
Red blood cells are a special type of cell that contain haemoglobin – this is a special iron-containing molecule that efficiently binds oxygen. When we breathe in and out, oxygen is taken out of the air in the lungs and is absorbed into the blood, being bound to haemoglobin in the RBCs. As these RBCs circulate around the body, the haemoglobin can then release the oxygen in the tissues of the body where it is vital to maintain life. Haemoglobin in the RBCs also gives blood its characteristic red colour.
When animals become anaemic, their ability to absorb oxygen from the air and deliver it to tissues in the body becomes very compromised and this can lead to many different problems, but is often manifested as weakness and lethargy. In severe cases, it will also cause an increased respiratory effort as the animal tries to get more oxygen in the lungs to improve the level of oxygen in the circulation.
Untreated, anaemia can be a debilitating disease, and if severe can be life-threatening. Unfortunately, cats are particularly prone to the development of anaemia. This is partly because their RBCs have a shorter lifespan (around 70 days) than many other animals (around 110-120 days in dogs and humans) – this means they have a higher turnover of RBCs and anaemia can, therefore, develop quite rapidly if anything interferes with this. Also, cats suffer from a number of different diseases and infections that can cause anaemia.
Types of anaemia
Anaemia can usually be broadly divided into regenerative and non-regenerative forms. Regenerative anaemias are those in which the bone marrow responds to the anaemia appropriately by trying to produce new RBCs to replace those that have been lost. However, in non-regenerative diseases, the anaemia develops because the bone marrow fails to produce new RBCs (or produces too few RBCs) to replace those that are being lost. In cats, sometimes multiple causes of anaemia can be present at the same time, which may complicate the picture.
Signs of anaemia
- Paleness or pallor – A common sign of anaemia in cats is paleness of the mucous membranes (these are the membranes – or ‘skin’ – lining the mouth and around the eyes etc). However, this is not an entirely reliable sign as pale membranes can also be seen for other reasons.
- Weakness – severe anaemia can cause weakness, and cats with anaemia will often be lethargic.
- Heart and breathing – anaemia, especially when severe, is likely to cause an increased heart rate (known as tachycardia), and an increased respiratory (breathing) rate (known as tachypnoea).
- Pica – anaemic cats often develop pica (a craving for unusual foods). Most commonly this is manifested as licking concrete, eating cat litter or eating soil.
- Jaundice – occasionally anaemic cats will also become jaundiced (yellow discolouration of the mucous membranes). This is most often a sign of liver disease in cats, but it can be seen with severe and sudden breakdown (haemolysis) of RBCs.
In addition to the signs associated with anaemia, cats may also show signs of an underlying disease (such as chronic kidney disease for example) that may be causing the anaemia. Cats that develop anaemia gradually over a long period are often able to adapt to the anaemia and show fewer signs (until the anaemia is really severe) compared with cats that develop a sudden onset of anaemia.
Severely anaemic cats may have very pale gums
Anaemia is confirmed by finding reduced RBC numbers (and reduced haemoglobin concentrations) in a blood sample collected from the cat. The reduced RBC numbers can be demonstrated directly using a machine that can count the individual cells, or can be detected more simply by a measurement call the ‘packed cell volume’ or PCV (this measurement can be obtained by spinning a small blood sample in a thin glass tube in a centrifuge, and observing the volume taken up by the RBCs which will sediment [or pack] at the bottom of the tube).
When anaemia is confirmed, the next step is to determine if it is regenerative or not. Features that indicate regeneration include:
- Variations in the size of RBCs (called anisocytosis) due to the presence of some larger and immature RBCs released from the bone marrow
- Presence of reticulocytes (immature RBCs) – using special stains these cells can be distinguished from normal (mature) RBCs, and by determining their number it is possible to gauge how regenerative the anaemia is.
Knowing whether the anaemia is regenerative or not will help in narrowing down the likely underlying cause of the anaemia. Regenerative anaemias are usually caused by either an increased breakdown of the RBCs (termed haemolysis) or by blood loss (eg, from bleeding excessively). Non-regenerative anaemias are usually caused by an underlying problem in the bone marrow preventing or interfering with the normal production of RBCs. Specific causes include:
Blood loss anaemia:
- Bleeding from an ulcerated mass or a tumour
- Bleeding due to poor blood clotting
Excessive bleeding may sometimes be very obvious, but can also be within the body or in the intestinal tract, for example, where it may be more difficult to detect.
- Feline leukaemia virus (FeLV) infection
- Mycoplasma haemofelis infection (feline infectious anaemia, formerly known as Haemobartonella felis infection), or other similar organisms
- Immune-mediated haemolytic anaemia (where the cat’s own immune system attacks the RBCs)
- Toxins, such as eating onions or onion-containing foods, paracetamol (acetaminophen)
- Increased fragility of RBCs, such as with a disease known as pyruvate kinase deficiency, seen particularly in Abyssinian and Somali cats
- Low blood phosphate levels
- Incompatible blood transfusions
- Neonatal isoerythrolysis – a condition seen in very young kittens where there is an incompatibility between the blood type of the kitten and the queen
- Feline leukaemia virus (FeLV) infection
- Feline immunodeficiency virus (FIV) infection
- Bone marrow failure
- Red cell aplasia (failure to produce RBCs)
- Leukaemia (cancer of the white blood cells that may affect the bone marrow)
- Chronic kidney disease
- Iron deficiency
- Chronic (long-standing) inflammatory diseases
Because of the wide variety of potential underlying causes of the different types of anaemia, further tests are often needed to identify the specific cause. These may include blood tests to identify infectious agents (such as FeLV, FIV and Mycoplasma haemofelis infections), tests to check the clotting ability of the blood, blood tests to check the iron status of the cat and to look for the presence of diseases such as chronic kidney disease. X-rays and/or ultrasound investigations may be needed in some cases, and if an underlying bone marrow problem is suspected then collection of bone marrow samples (a bone marrow aspirate or biopsy) may be required – this is a procedure that can be performed by simply placing a needle into a bone under a short general anaesthetic.
Treatment of anaemia will be both symptomatic and supportive for the affected cat, and specific (targeted at the underlying disease itself).
Supportive treatment may include the use of blood transfusions when the anaemia is severe as this can be a life-saving procedure. Just as in humans, it is important in cats to know what blood group the donor and recipient are to make sure the blood is compatible. With severe anaemia, a cat may need to be hospitalised and monitored closely.
A variety of treatments may be used depending on the specific underlying cause of the anaemia, and these may include antibiotics for some infectious causes (such as Mycopalsma haemofelis), immunosuppressive drugs (such as corticosteroids) if there is immune-mediated destruction of RBCs, iron supplementation for iron deficiency anaemia etc.
The prognosis in cases of anaemia varies depending on the cause. Many may respond well to treatment, but in some cases (especially severe non-regenerative anaemias caused by bone marrow disease) the long-term prognosis may be very guarded.