Monitoring high-dose heparin levels by ACT and HMT during extracorporeal circulation: diagnostic accuracy of three compact monitors

Abstract

The correct monitoring of heparin therapy and its reversal determines the successful conduct of cardiovascular surgery with extracorporeal circulation (ECC). The activated coagulation time (ACT) and the heparin management test (HMT) are the most frequently used tests in the operating room. Three compact monitors for ACT or HMT are here evaluated. Forty samples were obtained, at 10-min intervals, from eight patients during ECC. The ACT or HMT was immediately performed using: Hemochron Junior™ ACT, CoaguCeck™ Pro (ACT) and Rapid Point Coag (HMT). Data were compared between them and with the heparin levels, measured as anti-Xa. The simple least squares linear regression among, respectively, Hemochron Junior ACT, CoaguCeck Pro ACT, Rapid Point Coag HMT and anti-Xa activity were i = 452.3, s = 15.2, Sy/x = 37.5, r = 0.18; i = 411.9, s = 22.1, Sy/x = 48.7, r = 0.21 and i = 479.4, s = 9.0, Sy/x = 9.3; r = 0.41. CoaguCeck Pro ACT results were above the upper detection limit (500 s) in 37 of 40 determinations. The comparison between ACT Hemocron and HMT Rapid Point Coag shows i = 35.7, s = 0.9, Sy/x = 35.4, r = 0.68, with a bias of 29.0 s (CI: 17.9-40.1), 95% of agreement between -41.5 s (CI: -60.7 to -22.3) and 99.5 s (CI: 80.4-118.7). Taking a concentration of 2.0 U/ml of heparin to discriminate between high- and low-risk conditions, receiver-operator characteristic (ROC) curve was used to rank the performance of the methods. Areas under the ROC curve± SE for Hemochron Junior ACT and Rapid Point Coag HMT were 0.629± 0.097 and 0.543± 0.096. The results obtained by HMT appear similar to those obtained by the ACT for monitoring high-dose heparin therapy in patients undergoing ECC. HMT appeared to perform better than ACT in measuring the heparin effect, while the ROC analysis gives a little more accuracy for ACT. Neither of the two methods is able to achieve enough evidence of diagnostic accuracy. Since these tests are widely used, and there are no laboratory alternatives, a real comparison with the outcome of the patients should be helpful for an evidence-based evaluation of these point-of-care tests.