Overview
Platelets are very small non-nucleated cells that derive from fragmentation of megakaryocytes. They play an important role in clot formation and haemostasis.
Normal Range
- 150 - 400 x 10⁹/L
Thrombocytosis
Thrombosis refers to an increase in circulating platelets. This may occur due to a myeloproliferative neoplasm, a reactive increase in platelet production, or a shift in platelets from the spleen into the circulation.
Causes of Thrombocytosis
Primary
- Myeloproliferative neoplasms - essential thrombocythaemia, polycythaemia vera, chronic myeloid leukaemia, myelofibrosis
Increased Production
- Infection
- Inflammation - autoimmune disease, major surgery, trauma, fracture, burns, pancreatitis, infarction
- Malignancy
- Drugs - adrenaline, corticosteroids, vinca alkaloids, thrombopoietin
- Acute haemorrhage
- Iron deficiency
Platelet Shift
- Hyposplenism - splenectomy, liver cirrhosis, coeliac disease, sickle cell disease, SLE
Thrombocytopaenia
Reduced circulating platelets.
Causes of Thrombocytopaenia
Reduced Production
- Congenital thrombocytopaenia - e.g. May-Hegglin, Bernard-Soulier
- 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
- Myelodysplasia
- B12 / folate deficiency
Increased Destruction
- Autoimmune thrombocytopaenia - immune thrombocytopaenic purpura (ITP), SLE, antiphospholipid syndrome, rheumatoid arthritis
- Alloimmune thrombocytopaenia - transfusion reaction
- Drug-induced immune thrombocytopaenia - heparin-induced thrombocytopaenia (HIT), quinine, bactrim, vancomycin, rifampin, paracetamol, NSAIDs, glycoprotein IIb/IIIa inhibitors
- Infection - HIV, hepatitis C, EBV, CMV, H pylori, sepsis
- Thrombotic microangiopathies - thrombotic thrombocytopaenic purpura (TTP), haemolytic-uraemic syndrome (HUS), disseminated intravascular coagulation (DIC), HELLP syndrome
- Gestation thrombocytopaenia
Splenic Sequestration
- Hypersplenism
Factitious
- Platelet clumping
- Haemodilution (e.g. massive transfusion)
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