Analytical and clinical performance of two cardiac troponin I immunoassays

Cardiac troponin I assays for Axsym (Abbott Diagnostics, Abbott Path, IL, USA) and Immune 1 (Bayer Corporation, Tarrytown, NY, USA) analysers were evaluated. Heparin plasma or serum could be used for both assays. Samples were stable for 24 h at ambient temperature, 3 days at 4-8 degrees C and 3 months at -20 degrees C. After 10 months' storage at -80 degrees C, the recoveries were well above 100% by both assays. Total coefficients of variation for Axsym assay were 9.0 %, 5.8 % and 5.3 % at concentrations of 2.6 mu g/l, 9.83 mu g/l and 34.3 mu g/l respectively; for Immune 1 these were 4.4 %, 1.6 % and 1.8 % at 2.3 mu g/l,6.27 mu g/l and 44.35 mu g/l respectively. It was greater than or equal to 20 % at concentration of < 0.5 mu g/l for Axysm assay and less than or equal to 0.15 mu g/l for Immune 1 assay. Recoveries were less than or equal to 90 % at less than or equal to 0.22 mu g/l on Axsym and at less than or equal to 1.47 mu g/l on Immune 1. Neither method showed significant interference with haemoglobin, bilirubin, triglycerides or rheumatoid factor. Correlation between the two methods was excellent (r = 0.997, Y (Axsym) = 4.2X (Immuno 1) +3.2). The highest concentrations detected in 50 healthy subjects were 0.3 mu g/l and 0.1 mu g/l by Axsym and Immune 1 methods, respectively. Twelve out of 43 renal failure patients had troponin I 0.13-0.9 mu g/l using Axsym method and 4 had levels of 0.07-0.13 mu g/l using Immune 1. In muscle trauma patients, troponin I was undefectable.