- Platelets are very small non-nucleated cells with fine granules that derive from fragmentation of megakaryocytes.
- Thrombocytosis is an increase in the number of circulating platelets. This may be primary, in the context of myeloproliferative neoplasms, or secondary to another process.
Causes of Thrombocytosis
- Myeloproliferative neoplasms - essential thrombocythaemia, polycythaemia vera, chronic myeloid leukaemia, myelofibrosis
- Inflammation - autoimmune disease, major surgery, trauma, fracture, burns, pancreatitis, infarction
- Post splenectomy
- Iron deficiency anaemia
- Acute haemorrhage
- Acute haemolysis
- Drugs - adrenaline, corticosteroids, vinca alkaloids, thrombopoietin
- Thrombocytopaenia refers to a reduction in the number of circulating platelets.
- In a patient with new thrombocytopaenia, look for platelet clumping and fibrin strands which may indicate a factitiously low platelet count, or pseudothrombocytopaenia.
Causes of Thrombocytopaenia
- Congenital thrombocytopaenia
- Bone marrow failure - aplastic anaemia, paroxysmal nocturnal haemoglobinuria
- Bone marrow suppression - cytotoxic chemotherapy, radiotherapy, alcohol abuse
- Bone marrow infiltration - leukaemia, multiple myeloma, lymphoma, metastasis, myelofibrosis
- B12 / folate deficiency
- HIV infection
- Idiopathic thrombocytopaenic purpura (ITP)
- Heparin-induced thrombocytopaenia (HIT)
- Drug-induced thrombocytopaenia - heparin, quinine, bactrim, vancomycin, rifampin, paracetamol, NSAIDs, glycoprotein IIb/IIIa inhibitors
- Immune thrombocytopaenia - SLE, antiphospholipid syndrome, rheumatoid arthritis, transfusion reaction
- Thrombotic microangiopathies - thrombotic thrombocytopaenic purpura (TTP), haemolytic-uraemic syndrome (HUS), disseminated intravascular coagulation (DIC)
- Infection - hepatitis C, EBV, CMV, H pylori, sepsis
- Pregnancy - gestation thrombocytopaenia, preeclampsia / HELLP syndrome
- Platelet clumping
- Haemodilution (e.g. massive transfusion)
Abnormal Platelet Size
- Platelets are normally very small in size, though occasionally large or giant platelets may be seen. Platelet anisocytosis refers to a significant variation in the size of platelets on a blood film.
- Large platelets - larger than normal size, though smaller than the size of red cells
- Giant platelets - larger in size than red blood cells
Causes of Large and Giant Platelets
- Inherited giant platelet disorders - e.g. Bernard-Soulier
- Myeloproliferative neoplasms
- Myelodysplastic syndrome
- In a patient with new or worsening thrombocytopaenia, look for clumping of platelets which would result in a factitiously low platelet count.