A proposed stoichiometrical calibration procedure to achieve transferability of D-dimer measurements and to characterize the performance of different methods

Background: There is little transferability between D-dimer levels obtained by different reagents today. This makes it difficult to compare results from different clinical studies. Objectives: We give a comprehensive proposal for calibration of D-dimer assays. All crucial steps and underlying assumptions are made explicit. Methods: The new approach is based on using a set of fibrinolysates of patient samples clotted and treated with tPA to obtain maximal conversion to D-dimers. Their expected maximal D-dimer concentrations are calculated stoichiometrically from their different fibrinogen values and the published molecular masses of fibrinogen and average D-dimer. The characteristics of five latex enhanced D-dimer immunoassays were also tested against early and late fibrin fragments using this procedure. These were produced by prolonged fibrinolysis of a set of patient samples of varying fibrinogen concentrations. Results: These varied typically between methods and lysis times. One of the methods showing the highest yield irrespective of lysis time was used for calibration. A linear standard curve with zero intercept and R-2 = 0.95 was obtained. Conclusion: Following this procedure will allow better transferability of D-dimer in future clinical trails. (c) 2005 The Canadian Society of Clinical Chemists. All rights reserved.