Heparin detection by the activated coagulation time: A comparison of the sensitivity of coagulation tests and heparin assays

Objective: Laboratory and point-of-care coagulation tests are frequently obtained to determine the presence of heparin after surgical procedures. The objective of this study was (1) to compare the sensitivity of the activated coagulation time (ACT), activated partial thromboplastin time (aPTT), protamine titration (Hepcon; HMS Medtronic, Hemotec, Englewood, CO), and thromboelastography (TEG) with heparin anticoagulation and (2) to determine how frequently residual heparin is present in the 24-hour period after heparin neutralization in cardiopulmonary bypass (CPB) patients. Design: A prospective study. Setting: A tertiary care university teaching center that performs more than 15,000 surgical procedures per year. Participants: Vascular surgical (n = 17) and CPB (n = 29). Interventions: In vascular surgical patients, coagulation tests (ACT, protamine titration [Hepcon], and TEG) were obtained before and 90 minutes after heparin (50 to 60 U/kg IV) and compared with heparin concentration determined by factor Xa inhibition assay. In cardiac surgical patients, ACT and heparin concentrations were measured after anesthesia induction, during CPB, after protamine neutralization, and 3 as well as 6 hours after CPB. In addition to heparin concentrations and ACT measures, platelet counts, fibrinogen levels, and bleeding times were determined before and 3 and 24 hours after CPB. Measurements 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) correlated with the factor Xa inhibitory assay for heparin (r² = 0,76). All 17 patients had an abnormal TEG (mean 'R' time = 81 ± 39 minutes) and a marked elevation of aPTT (135 ± 35 sec [normal 22 to 33 seconds]) 90 minutes after heparin. In CPB patients, ACT did not correlate with heparin assays. After protamine neutralization of heparin in CPB patients, ACT returned to baseline despite the presence of heparin in 3 of 29 patients (0.22, 0.18, and 0.33 U/mL). Conclusions: ACT was less sensitive to residual heparin anticoagulation than aPTT, TEG, and whole blood heparin assay. The whole blood heparin assay (Hapcon) provided sensitive and specific data about the presence of residual heparin. Despite the limitation of ACT in detecting heparin, the investigators found that residual heparin was not common in the period after uncomplicated CPB.