<prompt> Best index of platelet function is:Bleeding timeClotting timeClot retraction timeProthrombin time  <response>: Bleeding time N 1-3 min is an index of platelet number. Bleeding time is prolonged when platelet number falls below 50,000mm3. Clot retraction is a function of platelets. The contractile filaments of platelets, in the platelet plug, are responsible for retraction of the clot that has formed on the surface of the platelet plug. Clot retraction occurs by 30-60 minutes after the formation of clot. 