Thrombocytopaenia is a condition in which there are too few platelets in the blood. Platelets are cells which help in clot formation. The normal platelet value ranges between 150,000 to 450,000/microL, and thrombocytopaenia is diagnosed at values below 150,000 platelets/microL.
Platelet numbers can be decreased by either reduced production in the bone marrow, or increased breakdown of cells.
Conditions of decreased production are:
- systemic infections, viral (rubella, mumps, hepatitis)or bacterial
- congenital or acquired bone marrow aplasia (non-functioning) such as Fanconi anaeamia, aplastic anaemia, leukaemia
- after chemotherapy, or irradiation to bone marrow
- vitamin B12 or folic acid deficiency
- direct alcohol toxicity
- HIV infection
Increased destruction is found in:
- ITP – due to platelet antibodies
- other immune destruction – for example after transfusion or transplantation
- thrombotic purpura
- disseminated intravascular coagulation – widespread clotting literally uses up available platelets
- hypersplenism – excessive platelet destruction in the spleen
- post infection – CMV and infectious mononucleosis
- physical destruction – by heart-lung bypass machines, or giant haemangiomas
- drug-induced – heparin, quinine and valproic acid are the best known
Symptoms and signs
Many patients have no symptoms and are diagnosed on routine testing for other problems. However, common symptoms are
- easy bruising or a characteristic rash (small purple spots called petechiae)
- nosebleeds or bleeding of the gums and inside the mouth
- menorrhagia – abnormally heavy menstrual bleeding
- prolonged bleeding after minor trauma such as a small cut
- severe cases may have frank bleeding into the intestines (vomiting blood or blood in the stool) or the brain (heamorrhagic stroke)
Diagnosis is by a blood test which shows a low platelet count. Establishing the cause of this may involve tests for antibodies, a clotting profile, and a bone marrow biopsy. A peripheral smear for detecting abnormalities of platelets and all other blood cells is essential.
This depends on the cause identified for example
- withdrawal of a causative drug
- removing the spleen
- immune suppression by steroids, chemotherapy or radiotherapy
- plasmapheresis to remove antibodies
- bone marrow transplant
Transfusion of platelets can be used to stop critical bleeding.