Evaluation of imprecision for cardiac troponin assays at low-range concentrations

BACKGROUND: The European Society of Cardiology/American College of Cardiology Committee for the Redefinition of Myocardial Infarction (MI) has recommended that an increased cardiac troponin should be defined as a measurement above the 99th percentile value of the reference group. A total imprecision (CV) at the decision limit of </=10% is recommended. However, peer-reviewed data on assay imprecision are lacking. The purpose of this study was to construct the clinically relevant imprecision profiles for each of the commercially available cardiac troponin assays. Pools of human sera containing cardiac troponin concentrations around the MI decision limit were assessed to identify the lowest concentration associated with a 10% CV. METHODS: Eight serum pools targeting different concentrations of cardiac troponin (I and T) were prepared and stored at -70 degrees C until usage. The cardiac troponin measurement protocol consisted of two replicates per specimen per run, and one run per day for 20 days, using two reagent lots and three calibrations. Manufacturers of each cardiac troponin assay directly performed the measurements. Data analysis for each assay was centralized and performed according to the NCCLS EP5-A guideline. RESULTS: The lowest concentrations (microg/L) providing a 10% CV were as follows: AxSYM, 1.22; ACS:180, 0.37; Centaur, 0.33; Immuno 1, 0.34; Access, 0.06; Vidas, 0.36; Liaison, 0.065; Dimension, 0.26; Opus, 0.90; Stratus CS, 0.10; Immulite, 0.32; Vitros ECi, 0.44; Elecsys, 0.04; AIA 21, 0.09. CONCLUSION: No cardiac troponin assay was able to achieve the 10% CV recommendation at the 99th percentile reference limit defined by the manufacturer.