Platelet Function
Bleeding time tests platelet function, not the intrinsic pathway. (Thrombin time tests the last step, fibrinogen to fibrin.)
Platelet Function
- Three major functions: Adhesion → Aggregation → Release + Amplification
- Platelet adheres to exposed subendothelium via VWF bridge (GPIb receptor) and collagen (GPIa)
- VWF = large glycoprotein; multimers of 2–50 dimeric subunits
- VWF synthesised by endothelial cells (stored in Weibel-Palade bodies) and megakaryocytes (stored in α granules)
- Ultra-large VWF multimers cleaved by ADAMTS13 metalloprotease → smaller multimers
Read this in Platelet Disorders
What our notes say
- Bleeding time tests platelet function, not the intrinsic pathway. (Thrombin time tests the last step, fibrinogen to fibrin.) (Internal Medicine CAT 1 (MBChB 4), 2022: liver, pancreas and bone marrow, 30 MCQ)
- Blood loss from poor platelet function (uraemic bleeding, gastrointestinal bleeding) and blood sampling. (Paediatrics end of fourth year main exam: 1 July 2019, Paper One, 99 of 100 MCQs)
- Platelet function studies show decreased aggregation in response to ADP, collagen, epinephrine, and thrombin. (Hematology MCQs)
- Platelet concentrate - concentrated platelets from whole blood or apheresis; for thrombocytopenia with bleeding, prophylaxis before invasive procedures and platelet function disorders (Haematology End of Year 2025 Past Paper — MKU MBML 3200 Questions & Answers)
- PFA-100 — modern test of platelet function under shear stress (Renal, Liver, Cardiac & Adrenal Function Tests for Year 3)
- Indication: thrombocytopenia with active bleeding, prophylaxis before invasive procedures in severely thrombocytopenic patients, platelet function disorders with bleeding (Haematology Exam 2025: MCQs on Anaemia, Leukaemia & Clotting)