New approach to standardisation of human cardiac Troponin I (cTnI)

Six different cTnI assays (5 commercial and one assay under development) were run with either their own calibrators or with standard dilutions of different forms of cTnI (free or complexed). Twenty-one serum samples from 7 AMI patients were analysed using these combinations of calibrators and assay constructs. The range of cTnI concentrations as measured in AMI serum samples by different assays was more than 10-fold using each assays own standards or when using free native or recombinant cTnI. With recombinant or in vitro formed ternary cTnI-cTnT-TnC complexes the differences were smaller (3-fold). The lowest between-manufacturer bias (1.4-fold) was obtained when the heart tissue derived native troponin complex was used for the calibration of the assays. For all assays, calibrated against this troponin I complex, the recalculated cut-off values were within 0.1-0.25 microgram/L. We conclude that to reduce assay-to-assay variation, native troponin complex is presently the preferred alternative for the standardisation of cTnI assays.