Impact of antibody specificity and calibration material on the measure of agreement between methods for cardiac troponin I

Background: Available assays for cardiac troponin I (cTnI) yield numericall y different results. The aim of this study was to compare patient values ob tained from four cTnI immunoassays. Methods: We studied the Stratus(R) II assay, the Opus(R) II assay, the Acce ss(R) assay, and a research-only cTnI heterogeneous immunoassay that uses t he Dade Behring aca(R) plus immunoassay system equipped with two new noncom mercial monoclonal antibodies. Because the aca plus cTnI assay is for resea rch only, we first evaluated and analytically validated it for serum and ci trated plasma. Initially; each method was calibrated using the method-speci fic calibrator supplied by each manufacturer; however, the aca plus cTnI as say was calibrated using patient serum pools containing cTnI and selected o n the basis of increased creatine kinase MB isoenzyme and with values assig ned by use of the Stratus cTnI assay. For method comparisons, individual pa tient sample cTnI values were determined and compared with the Stratus IT a ssay. Results: Passing and Bablock regression analysis yielded slopes of 1.44 (r = 0.96; n = 72) for the Opus II vs Stratus II assays; 0.07 (p = 0.91; n = 7 2) for the Access vs Stratus II assays; and 0.90 (u = 0.91, n = 72) for the aca plus vs Stratus II assays. The recalibration of each method with a Str atus II-assigned serum pool improved, but did not entirely eliminate, the s lope differences between the different assays (range, 1.00-1.16). The obser ved scatter in the correlation curves remained. Conclusion: There is a need to further explore the specificities of these a ssays with respect to the different circulating forms of cTnI. (C) 1999 Ame rican Association for Clinical Chemistry.