Expansion
Reduced production, increased destruction, sequestration or spurious
Expansion
Spurious
- EDTA induced platelet clumping, seen on the film. Repeat in citrate
- Clotted or dilute sample
Reduced production
- Marrow failure: aplastic anaemia, myelodysplasia, leukaemia, infiltration
- B12 or folate deficiency
- Alcohol, which is directly toxic to megakaryocytes
- Drugs, chemotherapy, radiotherapy
- Viral infection, including HIV, hepatitis C, Epstein-Barr virus
Increased destruction or consumption
- Immune thrombocytopenia, a diagnosis of exclusion
- Disseminated intravascular coagulation
- Thrombotic thrombocytopenic purpura and haemolytic uraemic syndrome
- Heparin induced thrombocytopenia
- Drugs: quinine, sulphonamides, penicillins, rifampicin, valproate
- Autoimmune disease, lymphoproliferative disease
- Pregnancy: gestational thrombocytopenia, HELLP
- Massive transfusion, mechanical destruction
Sequestration: hypersplenism from portal hypertension or any splenomegaly.
The two that must not be missed
- Heparin induced thrombocytopenia: a fall of over 50 per cent at 5 to 10 days of heparin, with thrombosis rather than bleeding. Stop all heparin including flushes and anticoagulate with an alternative
- Thrombotic thrombocytopenic purpura: thrombocytopenia with microangiopathic haemolysis, fever, renal impairment and neurological signs. Platelet transfusion is contraindicated and it needs urgent plasma exchange
Bleeding risk is generally low above 50, and spontaneous bleeding uncommon above 20.