<prompt> Extrinsic system of coagulation is checked by:March 2010aPTTPTBTPTT  <response>: Ans. B: PTBleeding Time Normal:1-6 min. is for checking the number of platelets. It is prolonged by lack of platelets. Clotting time Normal:6-10 min. varies widely depending upon the method employed, so discarded nowadays. Instead measurements of clotting factors are being done.aPTTPTT is employed for assessing intrinsic system.Prothrombin time Normal:12 sec. gives an good indication of concentration of prothrombin in the blood. Extrinsic pathway is assessed. 