HEPARIN DETECTION BY THE ACTIVATED COAGULATION TIME - A COMPARISON OFTHE SENSITIVITY OF COAGULATION TESTS AND HEPARIN ASSAYS

Objective: Laboratory and point-of-care coagulation tests are frequent ly obtained to determine the presence of heparin after surgical proced ures. The objective of this study was (1) to compare the sensitivity o f the activated coagulation time (ACT), activated partial thromboplast in time (aPTT), protamine titration (Hepcon; HMS Medtronic, Hemotec, E nglewood, CO), and thromboelastography (TEG) with heparin anticoagulat ion and (2) to determine how frequently residual heparin is present in the 24-hour period after heparin neutralization in cardiopulmonary by pass (CPB) patients. Design: A prospective study. Setting: A tertiary care university teaching center that performs more than 15,000 surgica l procedures per year. Participants: Vascular surgical (n = 17) and CP B (n = 29). Interventions: In vascular surgical patients, coagulation tests (ACT, protamine titration [Hepcon], and TEG) were obtained befor e and 90 minutes after heparin (50 to 60 U/kg IV) and compared with he parin concentration determined by factor Xa inhibition assay. In cardi ac surgical patients, ACT and heparin concentrations were measured aft er anesthesia induction, during CPB, after protamine neutralization, a nd 3 as well as 6 hours after CPB. In addition to heparin concentratio ns and ACT measures, platelet counts, fibrinogen levels, and bleeding times were determined before and 3 and 24 hours after CPB. Measurement s and Main Results: Ninety minutes after heparin, significant heparin concentrations were present in all vascular surgical patients, but ACT was elevated in only 4 of 17 patients. Protamine titration (Hepcon) c orrelated with the factor Xa inhibitory assay for heparin (r(2) = 0.76 ). All 17 patients had an abnormal TEG (mean ''R'' time = 81 +/- 39 mi nutes) and a marked elevation of aPTT (135 +/- 35 sec [normal 22 to 33 seconds]) 90 minutes after heparin. In CPB patients, ACT did not corr elate with heparin assays. After protamine neutralization of heparin i n CPB patients, ACT returned to baseline despite the presence of hepar in in 3 of 29 patients (0.22, 0.18, and 0.33 U/mL). Conclusions: ACT w as less Sensitive to residual heparin anticoagulation than aPTT, TEG, and whole blood heparin assay. The whole blood heparin assay (Hepcon) provided sensitive and specific data about the presence of residual he parin. Despite the limitation of ACT in detecting heparin, the investi gators found that residual heparin was not common in the period after uncomplicated CPB. Copyright (C) 1997 by W.B. Saunders Company.