Pitfalls in special coagulation testing: three illustrative case studies

Assays in the special coagulation laboratory are affected by numerous factors, including pre-analytical variables, anticoagulant drugs, and abnormalities of the coagulation system other than the analyte specifically being examined. By reviewing special coagulation tests as a group and in concert with clinical information, as well as understanding assay methodologies, interferences can be more easily recognized and incorrect interpretations avoided, preventing possibly unnecessary treatment of patients. Three case studies involving protein S activity, von Willebrand factor analysis, and factor V activity with Bethesda titer will highlight potential pitfalls in the interpretation of special coagulation tests.