Screening tests of the hemostatic system.

The hemostatic system consists of the subcutaneous tissue/vessel wall/platelet system and the coagulation cascade. Hemostasis occurs initially through the interaction between circulating platelets and subendothelial collagen, so that a platelet plug is formed. The platelet plug produces hemostasis, but is unstable and will disintegrate unless the coagulation cascade generates fibrin. The presence of the fibrin in the plug results in permanent hemostasis. The five tests of hemostasis - platelet count, bleeding time, partial thromboplastin time, prothrombin time and Factor XIII assay - are described.