Effect of aprotinin on activated clotting time whole blood and plasma heparin measurements

Twenty cardiac surgical patients requiring cardiopulmonary bypass were enrolled in this study designed to evaluate the effect of aprotinin on activated clotting time (kaolin and celite), whole blood, and laboratory-based plasma (anti-Xa) heparin measurements. Whole blood heparin measurements were not different (p = 0.98) between aprotinin-treated (3.2 ± 2.8 U/mL) and control (3.2 ± 3.0 U/mL) specimens. Plasma anti-Xa heparin measurements were also not different (p = 0.95) between aprotinin-treated (2.7 ± 2.5 U/mL) and control (2.8 ± 2.5 U/mL) specimens. The relationship between whole blood (plasma equivalent) and plasma heparin measurements was similar (p0 = 0.1) in the presence (slope, 1.04; r2 =0.89) or absence (slope, 1.11; r2 = 0.89) of aprotinin. In contrast to weak correlations between celite (r = 0.50) or kaolin (r = 0.53) activated clotting time values, whole blood heparin measurements correlated well (r = 0.93) with plasma heparin measurements during cardiopulmonary bypass in the presence of aprotinin. These findings indicate that whole blood heparin measurements are unaffected by aprotinin and correlate well with plasma anti-Xa heparin measurements even in the presence of aprotinin. Therefore, the automated protamine titration assay can be used to monitor accurately heparin concentrations in patients receiving aprotinin.