Performance and Interpretation of Routine Coagulation Assays

Hemostasis is a physiologic response to vascular injury involving the coagulation system, platelets, endothelial cells, and the vascular wall. Activation of the proteins of the coagulation system leads to the formation of thrombin and the conversion of fibrinogen into an insoluble fibrin clot. Abnormalities of the coagulation system can be detected by routine coagulation assays that include the prothrombin time (PT/INR), activated partial thromboplastin time (APTT), fibrinogen assay, and thrombin time. This chapter covers the laboratory performance of basic coagulation testing and discusses interpretation of testing results for diagnosis of bleeding disorders. The chapter also includes a discussion of assuring quality in the hemostasis laboratory through assay validation, setting appropriate reference ranges, internal quality control, and external quality assessment.