Platelet Count
Platelets initiate clotting at sites of vascular injury. Both very low (bleeding risk) and very high (thrombosis risk) values matter clinically — bone-marrow disease, immune destruction or reactive elevation are the leading causes.
What it measures
Platelets (thrombocytes) are cell fragments produced by megakaryocytes in the bone marrow. They are first responders at sites of vascular injury, forming the initial platelet plug before the clotting cascade reinforces it with fibrin. A normal blood platelet count is 150–450 × 10⁹/L. Spurious results from EDTA-induced platelet clumping are common — when an isolated low count is reported, repeat with a citrate tube before drawing conclusions.
What a high value can mean
- Reactive thrombocytosis — most common; inflammation, infection, iron deficiency, post-splenectomy.
- Essential thrombocythaemia — bone-marrow disorder; usually >600 × 10⁹/L with JAK2 mutation in many.
- Polycythaemia vera — often with high red cell count too.
- Recovery from acute illness or chemotherapy — rebound rise.
What a low value can mean
- Immune thrombocytopenia (ITP) — autoimmune destruction.
- Bone-marrow suppression — chemotherapy, alcohol, B12/folate deficiency, leukaemia, aplastic anaemia.
- Increased consumption — DIC, sepsis, HUS, TTP.
- Hypersplenism — sequestration in cirrhosis, lymphoma.
- Heparin-induced thrombocytopenia — drug-mediated.
- EDTA pseudothrombocytopenia — laboratory artefact, always confirm with citrate tube.
When to discuss with a doctor
Platelet count <100 × 10⁹/L warrants a primary-care visit and repeat with citrate tube. <50 × 10⁹/L carries spontaneous bleeding risk and needs prompt evaluation. >1000 × 10⁹/L warrants haematology evaluation for myeloproliferative disease. Mediora.AI tracks the platelet trajectory in the context of haemoglobin and WBC.