Coagulation and Transfusion Medicine / POCT FOR PROTHROMBIN TIME CORRELATES WITH LABORATORY PROTHROMBIN TIME

Point-of-care testing (POCT) of coagulation parameters can help optimize transfusion practice in cardiac surgery. Antifibrinolytic agents may interfere with the laboratory and/or POCT coagulation assays. This randomized controlled study compared coagulation parameters obtained from a whole blood POCT coagulation device with a typical laboratory instrument in cardiac surgery patients receiving aprotinin, epsilon-aminocaproic acid, or normal saline before undergoing cardiopulmonary bypass. Aliquots of arterial blood samples from 42 patients were collected perioperatively, and their prothrombin times (PTs) and activated partial thromboplastin times (aPTTs) were measured by POCT and laboratory instrumentation. Linear regression and error analyses were used for the method comparison. For PT, the POCT device compared favorably with the laboratory method. For aPTT, the POCT device did not compare well with the laboratory method. Treatment with antifibrinolytic agents does not interfere with determination of PT. Bleeding diathesis after cardiac surgery is multifactorial and often has adverse consequences in terms of morbidity and mortality. Point-of-care testing (POCT) can provide a rapid turnaround time for prothrombin time (PT) and activated partial thromboplastin time (aPTT). These rapidly available data not only help to differentiate surgical bleeding from underlying coagulopathy but also have a crucial role in the appropriate use of blood components.1-4 The correlation of POCT and laboratory PT and a PTT has been quite variable depending on the assay used, the clinical context, or both. Previous studies have shown that POCT PT results compared well with those obtained from laboratory instrumentation for patients undergoing cardiac operations without antifibrinolytic therapy.4-6 Aprotinin, a bovine protein that is a broad-spectrum serine protease inhibitor, and epsilon-aminocaproic acid (EACA), a lysine analogue that inhibits plasmin activity and fibrinolysis, are being used for the vast majority of cardiac surgery patients to reduce blood loss.7-11 This raises the concern that antifibrinolytic agents such as aprotinin and EACA may interfere with the determination of PT, aPTT, or both using laboratory or POCT methods. Indeed, Despotis et al12 demonstrated a dose-dependent prolongation of whole blood aPTT when aprotinin was added in vitro to specimens obtained before and after cardiopulmonary bypass (CPB). Therefore, before POCT devices can be used for patients receiving aprotinin or EACA during cardiac surgery, they must have a one-to-one, first-order, monotonic, linear transformation with typical laboratory instruments,13 and the ex vivo effect of these antifibrinolytics on any laboratory or POCT coagulation assays should be studied. The present study compared CoaguChek Plus (Roche, Indianapolis, IN), a whole blood POCT coagulation assay, with the ACL 6000 coagulation Coagulation and Transfusion Medicine / ORIGINAL ARTICLE Am J Clin Pathol 2002;117:74-78 75 © American Society for Clinical Pathology analyzer (Instrumentation Laboratory, Lexington, MA), a laboratory method, for specimens collected from cardiac surgery patients receiving aprotinin or EACA. Materials and Methods