Standardization of troponin I measurements: an update

Standardization of cardiac troponin I (cTnl) measurement is important because of the central role for diagnosis of myocardial infarction. In blood, cTnl is present as a heterogeneous mixture of different molecular species. The analytical problem caused by this heterogeneity may be circumvented by recognition of a unique, invariant part of the molecule that is common to all components of the mixture. Antibodies used for the development of cTnl assays should selectively recognize epitopes within this invariant part, leading to a consequential increase in the homogeneity of immunoassay reactivity. This should be associated with the use of a reference material that represents the natural and major antigen in blood after tissue release, i.e., the troponin complex. Although a primary reference material for cTnl is available, studies indicate that cTnl assays remain without harmony after recalibration using this material. To achieve closer comparability of cTnl values between assays, the use of a secondary reference material, consisting of a panel of human serum pools, is proposed for use by manufacturers to calibrate their assays. To assign true cTnl concentration values to this secondary reference material, establishment of a reference measurement procedure for cTnl is required. A practical approach to the development of a reference procedure could be to design an immunochemical assay with well-characterized specificity to the invariant part of the cTnl molecule and calibrated using the primary reference material.