Dog - Lack of Blood Platelets - Thrombocytopaenia

What are blood platelets?

Blood platelets, scientifically known as thrombocytes, are produced from the largest cells found in the bone marrow (megakaryocytes). One megakaryocyte will produce many platelets. Once in circulation they usually survive for 10-12 days. At the site of any damage to a blood vessel they form a plug reducing blood loss, and liberating thromboplastin, an enzyme, which acts in the clotting process.

What is thrombocytopaenia?

This term indicates there is a decrease in the number of circulating blood platelets thus impairing blood clotting.

Why is this serious?

Once thrombocytopaenia occurs even a minor injury can result in uncontrollable bleeding.

What are the main causes?

• Haemorrhage. If your dog has had a major haemorrhage (bleed) for any reason, platelet numbers are decreased until the bone marrow replenishes them. This usually only takes 2-3 days in a healthy dog.
• Infection. Infections such as ehrlichiosis (see separate client handout) can result in decreased platelet production by the bone marrow.
• Drugs. Drugs such as oestrogens (female hormones), certain antibiotics and some analgesics (pain killers) can be responsible.
• Neoplasia. Some forms of cancer will cause thrombocytopaenia.
• Chronic renal disease. This is not an uncommon cause of problems in older dogs.
• Immune problems. Immune mediated thrombocytopaenia causes destruction of platelets.

Lack of platelets should not be confused with platelet dysfunction such as occurs in von Willebrand’s disease. This is an hereditary condition affecting German Shepherd Dogs and certain other breeds. It results in platelets not clumping properly when vessels are damaged due to a deficiency of von Willebrand’s factor in the blood.

What does treatment involve?

This will depend on the cause of the thrombocytopaenia. Since blood clotting will be inefficient, it is important to minimise risk of haemorrhage. Strict rest, gentle handling and avoidance of any elective surgery is paramount.

In an emergency blood transfusions will be used but this is only a temporary solution since healthy platelets only live approximately 10 days and are then removed by the spleen, liver and bone marrow.

In cases of immune mediated thrombocytopaenia drugs including corticosteroids may be used.

Some infections, including ehrlichiosis respond well to antibiotics. If the lack of platelets is found to be due to the use of drugs for another purpose a change of therapy will often result in dramatic improvement.

You mentioned immune mediated thrombocytopaenia (IMT), what is this?

Also known as idiopathic thrombocytopaenic purpura (ITP). It is one of the most common acquired causes of defective clotting in the dog. A rare disease, it causes low numbers of circulating platelets because the body mounts an antibody defence against its own blood platelets. It is one of a collection of immune mediated diseases.

Autoimmune haemolytic anaemia, (AIMHA) is associated with the production of auto antibodies against red blood cells (erythrocytes). This is the commonest cause of haemolytic anaemia in the dog. It has been reported to occur, but very rarely, following certain booster vaccinations. IMHA and IMT can be part of other disorders, e.g. systemic lupus erythematosus (SLE) in which thrombocytopaenia, together with polyarthritis are often the main signs.

Can these immune disorders be treated?

Yes. Corticosteroids and other immunosuppressant drugs play an important role in the control of these conditions.