Reliability of the Heparin Management Test for Monitoring High Levels of Unfractionated Heparin: In Vitro Findings in Volunteers versus In Vivo Findings during Cardiopulmonary Bypass

Background: The authors assessed the heparin management test in vitro in volunteers and in vivo during cardiopulmonary bypass.

Methods: In vitro, the heparin management test was analyzed for heparin levels between 0 and 6 IU/ml using variations in hematocrit, platelets, procoagulants, and storage time. The in vivo studies consisted of two groups: In group I (cardiopulmonary bypass <= 90 min, n = 40), anticoagulation was performed according to the activated clotting time (with or without aprotinin); in group II (cardiopulmonary bypass >= 180 min, with aprotinin) included use (n = 10) and nonuse of coumadin (n = 10) and anticoagulation according to the automated heparin dose-response assay. Tests were performed in duplicate (whole blood, two heparin management test analyzers) and compared with anti-Xa activity (plasma).

Results: In vitro, the results of the heparin management test (n = 1,070) correlated well with heparin concentration (r2 = 0.98). Dilution and storage time did not affect the heparin management test; a hematocrit of 60% and reduced procoagulants (10%) prolonged clotting time. In vivo, the correlation (heparin management test vs. anti-Xa) was strong in group I (r2 = 0.97 with aprotinin] and 0.96 without aprotinin]; n = 960) and group II without coumadin (r2 = 0.89, n = 516). In group II with coumadin, the overall correlation was r2 = 0.87 and 0.79 (n = 484), although the range varied widely (0.57-0.94, between-analyzer differences 0-47%).