Normal clot retraction time is 0-2 hours. If the weight of the clot or the percent of extruded serum is used as the end measure, the result depends on the volume of the specimen used, which varies from laboratory to laboratory.
The coagulation cascade is complex. Platelets play a major role to initiate the process and regulate it through biochemical and mechanical interactions. The 3 steps of this process for platelets are adhesion, aggregation, and finally, retraction.
The clot retraction study measures the time taken for a platelet plug to undergo this last step, which indicates overall platelet function.