Determination of normal versus abnormal activated partial thromboplastin time and prothrombin time after cardiopulmonary bypass

Abstract

Objective: The study's objective was to determine the prothrombin time (PT) and activated partial thromboplastin time (aPTT) values that differentiated normal from excessively bleeding patients immediately after cardiopulmonary bypass (CPB).

Design: A prospective blinded study.

Setting: A large academic medical center.

Participants: 148 patients were studied.

Interventions: aPTT and PT were determined by the hospital laboratory and the Biotrack 512 Coagulation Monitor (Ciba Corning Diagnostics, Medfield, MA) from an arterial whole blood sample obtained 10 minutes after protamine administration. Patients were subjectively and objectively defined as "bleeders" or "nonbleeders" with blinded observers.

Measurements and main results: The specificity and sensitivity were determined by a receiver operating characteristic (ROC) analysis. Twenty-three of 148 patients (14.9%) were characterized as bleeders. The laboratory PT had a maximal specificity and sensitivity of 78% and 75%, respectively, at a value of 15.4 s, with a negative and positive predictive value of 93% and 33%, respectively. The maximal specificity and sensitivity of the laboratory aPTT was 64% and 76%, respectively, at a value of 46 s, with a negative and positive predictive value of 89% and 33%, respectively. aPTT and PT approached normal values after 12 hours in the intensive care unit.

Conclusion: The aPTT and PT values that produce the maximal sensitivity and specificity in the ROC analysis may be helpful to differentiate patients who are bleeding excessively from those patients who are not after CPB and to guide transfusion of blood products. New whole blood coagulation devices with rapid turn-around times had similar predictive value for bleeding tendency compared with standardized laboratory tests.