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 vo lunteers and in vivo during cardiopulmonary bypass. Methods: In vitro, the heparin management test was analyzed for heparin lev els between 0 and 6 IU/ml using variations in hematocrit, platelets, procoa gulants, and storage time, The in vivo studies consisted of two groups: In group I (cardiopulmonary bypass less than or equal to 90 min, n = 40), anti coagulation was performed according to the activated clotting time (with or without aprotinin); in group II (cardiopulmonary bypass greater than or eq ual to 180 min, with aprotinin) included use (n = 10) and nonuse of coumadi n (n = 10) and anticoagulation according to the automated heparin dose-resp onse assay. Tests were performed in duplicate (whole blood, two heparin man agement test analyzers) and compared with anti-Xa activity (plasma). Results: In vitro, the results of the heparin management test (n = 1,070) c orrelated well with heparin concentration (r(2) = 0.98). Dilution and stora ge time did not affect the heparin management test; a hematocrit of 60% and reduced procoagulants (10%) prolonged clotting time. In vivo, the correlat ion (heparin management test vs. anti-Xa) was strong in group I (r(2) = 0.9 7 [with aprotinin] and 0.96 [without aprotinin]; n = 960) and group n:witho ut coumadin (r(2) = 0.89, n = 516), In group II with coumadin, the overall correlation was r(2) = 0.87 and 0.79 (n = 484), although the range varied w idely (0.57-0.94, between-analyzer differences 0-47%). Conclusions: The results of the heparin management test were influenced by hematocrit, plasma coagulation factors, and the heparin level, but not by u se of aprotinin. The heparin management test provided reliable values in vi tro in group I, and in group II without coumadin but was less reliable in g roup II with coumadin.