Thrombin time (TT) and prothrombin time (PT) are two different clinical measures of blood plasma coagulation.
Both clotting tests end with the conversion of fibrinogen to fibrin; however, the TT skips directly to this conversion by adding thrombin reagent, while PT involves the entire extrinsic pathway. Despite the fact that PT involves the same clotting steps as TT plus several others, the normal range for TT is slightly longer than the normal range for PT.
Why is the normal range for TT longer than the normal range for PT when the former skips several clotting steps? Without background information about the normal ranges, it seems much more logical for the prothrombin clotting test to take longer.
