Standardization of cardiac troponin I assays: Round robin of ten candidate reference materials

Background: Cardiac troponin I (cTnI) results vary 100-fold among assays. As a step toward standardization, we examined the performance of 10 candidate reference materials (cRMs) in dilution studies with 13 cTnl measurement systems. Methods: Solutions of 10 cTnI cRMs, each characterized by NIST, were shipped to the manufacturers of 13 cTnI measurement systems. Manufacturers used their respective diluents to prepare each cRM in cTnI concentrations of 1, 10, 25, and 50 μg/L. For the purpose of ranking the cRMs, the deviation of each cTnI measurement from the expected response was assessed after normalization with the 10 μg/L cTnI solution. Normalized deviations were examined in five formats. Parameters from linear regression analysis of the measured cTnI vs expected values were also used to rank performance of the cRMs. Results: The three cRMs demonstrating the best overall rankings were complexes of troponins C, I, and T. The matrices for these three cRMs values differed; one was reconstituted directly from the lyophilized form submitted by the supplier; one was submitted in liquid form, lyophilized at NIST, and subsequently reconstituted; and the third was evaluated in the liquid form received from the supplier. The cRM demonstrating the fourth best performance was a binary complex of troponins C and I supplied in lyophilized form and reconstituted before distribution. Conclusions: The cRMs demonstrating the best performance characteristics in 13 cTnI analytical Systems will be included in subsequent activities of the cTnI Standardization Committee of the AACC.