Comparison of three methods for measuring PEG-hirudin in blood

Three methods for measuring pegylated hirudin (PEG-hirudin), a new antithrombotic agent, in blood were compared using clinical samples. The ecarin clotting time (ECT) was performed in whole blood using a point-of-care device (TAS analyzer). The ECT was also performed in plasma, using a clotting assay in a conventional automated coagulation analyzer. Finally, a chromogenic method was used, based on thrombin inhibition and the substrate S-2238. Both clotting assays showed a linear relationship between the ECT and the PEG-hirudin concentration up to 3.0 microg/ml. The chromogenic substrate method was linear only between 0.1 and 1.0 microg/ml PEG-hirudin. The intra-assay coefficient of variation was 3.0% for the automated ECT method, 6.4% for the point-of-care ECT method and 3.4% for the chromogenic method. The inter-assay coefficient of variation was approximately 10% for both clotting methods and 3.2% for the chromogenic method. There was a high correlation (r = 0.954) in PEG-hirudin concentration between both ECT methods over the entire measuring range. The correlation of the chromogenic method with any ECT was significantly less (r < 0.89), even if only PEG-hirudin concentrations < 1.0 microg/ml were taken into account (r < 0.92). Although we clearly prefer the conventional ECT, any of the other methods may be used for monitoring PEG-hirudin in patients treated with this drug, depending on the specific application and local circumstances.