Laboratory testing issues for protein C, protein S, and antithrombin.

Thrombophilia is a complex disease process, which clinically expresses as venous thrombosis. The presence of a genetic defect in one of the major contributing components (protein C [PC], protein S [PS], and antithrombin [AT]) to thrombophilia can be determined by clinical laboratory assays. However, understanding the limitations and problems associated with assays is paramount to an accurate analysis of the genetic status. This review will discuss the major analytical issues and provide recommendations for assaying PC, PS, and AT in plasma. Recommendations are also made about pre-analytical and postanalytical issues clinically affecting these assays.

The effect of instrumentation and laboratory site on the accuracy of the APTT-based heparin therapeutic range.

BACKGROUND: Monitoring of unfractionated heparin therapy by activated partial thromboplastin time using the ex vivo method for determining the heparin therapeutic range (HTR) is the standard of practice. Many extrinsic and intrinsic factors influence accuracy of the HTR. This study investigates the affect of instrumentation and laboratory site on the accuracy of the ex vivo HTR method. METHODS: Patients on unfractionated heparin are used to determine the HTR by published guidelines. Various instruments and different laboratories are compared to investigate the affect of these variables on the HTR. RESULTS: The HTR is the same when the same model of instrument or even different models (same methodology) are used in the same laboratory. However, a significant clinical difference is observed when different hospital laboratories using same lot and instrument model are compared. CONCLUSIONS: The ex vivo method for HTR is the best protocol currently available. The HTR should be determined and averaged on all of the same method instruments used in the laboratory. However, determination of the HTR in different laboratories should not be shared.