Standardization of cardiac troponin I assays: Round robin of ten candidatereference materials

Background: Cardiac troponin I (cTnI) results vary 100-fold among assays. A s a step toward standardization, we examined the performance of 10 candidat e reference materials (cRMs) in dilution studies with 13 cTnI measurement s ystems. Methods: Solutions of 10 cTnI cRMs, each characterized by NIST, were shippe d to the manufacturers of 13 cTnI measurement systems. Manufacturers used t heir respective diluents to prepare each cRM in cTnI concentrations of 1, 1 0, 25, and 50 mug/L,. For the purpose of ranking the cRMs, the deviation of each cTnI measurement from the expected response was assessed after normal ization with the 10 mug/L cTnI solution. Normalized deviations were examine d in five formats. Parameters from linear regression analysis of the measur ed cTnI vs expected values were also used to rank performance of the cRMs. Results: The three cRMs demonstrating the best overall rankings were comple xes of troponins C, I, and T. The matrices for these three cRMs values diff ered; one was reconstituted directly from the lyophilized form submitted by the supplier; one was submitted in liquid form, lyophilized at NIST, and s ubsequently reconstituted; and the third was evaluated in the liquid form r eceived from the supplier. The cRM demonstrating the fourth best performanc e was a binary complex of troponins C and I supplied in lyophilized form an d reconstituted before distribution. Conclusions: The cRMs demonstrating the best performance characteristics in 13 cTnI analytical systems will be included in subsequent activities of th e cTnI Standardization Committee of the AACC, (C) 2001 American Association for Clinical Chemistry.