The harmonization of cardiac troponin I measurement is independent of sample time collection but is dependent on the source of calibrator

We compared the agreement of cardiac troponin I (cTnI) values between seven cTnI assay systems in clinical samples collected from 1 h up to 11 days post acute coronary syndrome (ACS), before and after correction for calibration differences between systems. Values were referenced to two sources of common calibrator, namely, a manufactured cardiac troponin material containing the ternary ICT complex, and a serum from an ACS-positive subject. In 38 samples, cTnI varied up to sevenfold between systems, the among-systems coefficient of variation ranging from 49% to 127%. After correction for method calibration differences by reference to the cTnICT material, the inter-method variation was 43% to 99% compared with 13% to 68% for the serum-based material. Differences in cTnI isoform composition between the materials, or matrix interactions for the cTnICT calibrator, might contribute to the variation in harmonization effect. Despite the improved comparability of test values by the use of the serum-based calibrator, there was a residual variation in test values between systems that was not attributable to the time of collection of the sample post ACS. We concluded that due to the heterogeneity of clinical samples, use of a pooled human serum material might better serve as a secondary reference reagent for cTnI measurement. (C) 2002 Elsevier Science B.V. All rights reserved.