Platelet Count
Overview
Platelet count measures the number of platelets (thrombocytes) circulating in blood, typically 150-450 × 10⁹/L, essential for hemostasis, clot formation, and vascular repair. Platelets aggregate at injury sites under von Willebrand factor and collagen guidance, releasing granule contents to activate coagulation. Elevated counts (thrombocytosis) indicate inflammation, iron deficiency, or myeloproliferative neoplasms; low counts (thrombocytopenia) suggest bone marrow failure, immune destruction, or sequestration. Clinically, platelet count guides bleeding risk assessment, transfusion decisions, and chemotherapy dosing.
Clinical Use Cases
- Diagnosing thrombocytopenia causes (ITP, TTP, HIT, DIC).
- Monitoring myeloproliferative neoplasms (ET, PV, CML).
- Assessing infection/inflammation-associated reactive thrombocytosis.
- Pre-procedure bleeding risk stratification.
Specimen Types
- Whole blood (EDTA anticoagulant preferred).
- Citrate plasma (for functional studies).
Measurement Methods
- Automated impedance hematology analyzer.
- Optical flow cytometry platelet counting.
- Manual phase contrast microscopy (low counts).
Test Preparation and Influencing Factors
- No fasting required; avoid prolonged tourniquet (>1 minute).
- Recent exercise, stress, or epinephrine elevate counts via demargination.
- Clotted specimens cause pseudothrombocytopenia.
- Giant platelets or platelet clumps require smear review.
Synonyms
- Thrombocyte count.
- PLT.