Determination of plasma aprotinin levels by functional and immunologic assays

We compared a functional (amidolytic) and an enzyme-linked immunosorbent as say (ELISA) method for determining aprotinin concentration in 82 plasma sam ples obtained from patients undergoing cardiac surgery with aprotinin thera py. There was good correlation between methods (r = 0.87); however, aprotin in measurements by chromogenic assay were significantly higher than by ELIS A [234 +/- 104 kallikrein inhibitory units (KIU)/ml versus 155 +/- 88 KIU/m l; P = 0.0001]. This appeared to be attributable to differences in the pote ncy of the material used to standardize the assays. When results were corre cted to allow for potency of the standard, there was no significant differe nce between chromogenic and ELISA methods (234 +/- 104 KIU/ml versus 240 +/ - 137 KIU/ ml), although the ELISA results tended to be higher in some samp les. These data suggest that aprotinin concentrations measured by these met hods cannot be used interchangeably, and care must be taken when interpreti ng data from studies measuring aprotinin. Blood Coagul Fibrinolysis 12:37-1 2 (C) 2001 Lippincott Williams & Wilkins.