Preanalytical Variables in the Coagulation Laboratory

Though cardiovascular disease remains the most common cause of death in Western countries, significant progress has been made in the management of it during the past 2 decades. Increased use of anticoagulant therapy has played an important role in the improved outlook for patients with occlusive arterial or venous thromboembolic disease. However, while anticoagulant drugs reduce a patient’s risk of heart attack and stroke by making the blood less clottable, this same effect increases the patient’s risk of hemorrhage. This necessitates laboratory monitoring of the patient’s response to these drugs on an ongoing basis. For instance, of the approximately 300 million coagulation tests performed annually in the United States, more than 40 million are prothrombin times (PT) performed for monitoring of warfarin therapy. While monitoring of anticoagulant therapy may have the most immediate impact on patient management and outcome, clinicians also rely heavily on the accuracy of screening and diagnostic PT and activated partial thromboplastin time (APTT) tests; platelet function studies; work-ups to identify inherited thrombotic predisposition; and measurement of coagulation factors and inhibitors, D-dimer, and other coagulation analytes. Because of the significantly improved instrumentation and highly sensitive reagents available in modern coagulation laboratories, preanalytical variability now represents the most important source of errors that can lead to inaccurate patient results, patient mismanagement, and preventable hemorrhagic or thrombotic complications. This article will review the importance of the quality and integrity of the coagulation sample for the accuracy and precision of patient test results, and discuss approaches to improve coagulation laboratory performance by controlling preanalytical variability.