Biological variation and reference change value of high-sensitivity troponin T in healthy individuals during short and intermediate follow-up periods.

BACKGROUND: Acute myocardial infarction is defined by a troponin concentration >99th percentile with an acute increase and/or decrease, the magnitude of which has not yet been well defined. To aid the interpretation of changes in cardiac troponin concentration, we sought to establish biological variation and reference change values (RCVs) by applying both the normal and lognormal approaches for cardiac troponin T (cTnT) sampled at hourly and weekly intervals in healthy individuals and measured on the Roche E 170 and Elecsys® 2010 automated platforms. METHODS: High-sensitivity cTnT (hsTnT) was measured at baseline, and after 1, 2, 3, and 4 h and after 1, 2, 3, and 4 weeks in 20 and 17 healthy individuals, respectively. A healthy status was established by physical examination, MRI analysis at rest and during dobutamine stress, lung function testing, and blood sample testing. RESULTS: Hourly total and within-individual CVs were 18% and 15%, respectively, for the E 170 assay, and 24% and 21%, respectively, for the Elecsys 2010 assay. Weekly total and within-individual CVs for these assays were 32% and 31%, respectively, for the E 170 assay, and 32% and 30%, respectively, for the Elecsys 2010 assay. The RCVs for the E 170 and Elecsys 2010 assays were ±46% and ±62% (hourly), respectively, and ±87% and ±86% (weekly), respectively. The corresponding lognormal values were +64%/-39% and +90%/-47% (hourly), and +138%/-58% and +135%/-58% (weekly). CONCLUSIONS: RCVs appear attractive for interpreting hsTnT results. The short-term biological variation of hsTnT is low but becomes somewhat more important at intermediate sampling intervals. Knowledge of this variation is important for interpreting results from patients in whom cTnT values increase from low concentrations.

Analytical validation of a high-sensitivity cardiac troponin T assay.

BACKGROUND: We report the development of a novel high-sensitivity cardiac troponin T (hs-cTnT) assay, a modification of the Roche fourth-generation cTnT assay, and validation of the analytical performance of this assay. METHODS: Validation included testing of analytical sensitivity, specificity, interferences, and precision. We established the 99th percentile cutoff from healthy reference populations (n = 616). In addition, we studied differences in time to a positive result when using serial measurements of hs-cTnT vs cTnT in patients with a confirmed diagnosis of non-ST elevation myocardial infarction (non-STEMI). RESULTS: The hs-cTnT assay had an analytical range from 3 to 10 000 ng/L. At the 99th percentile value of 13.5 ng/L, the CV was 9% using the Elecsys 2010 analyzer. The assay was specific for cTnT without interferences from human cTnI or cTnC, skeletal muscle TnT, or hemoglobin concentrations up to 1000 mg/L, above which falsely lower values would be expected. When the assay was evaluated clinically, a hs-cTnT higher than the 99th percentile concentration identified a significantly higher number of patients with non-STEMI on presentation (45 vs 20 patients, P = 0.0004) compared with cTnT, and a final diagnosis of non-STEMI was made in 9 additional patients (55 vs 46 patients, P = 0.23) after serial sampling. Time to diagnosis was significantly shorter using hs-cTnT compared with cTnT [mean 71.5 (SD 108.7) min vs 246.9 (82.0) min, respectively; P < 0.01]. CONCLUSIONS: The analytical performance of hs-cTnT complies with the ESC-ACCF-AHA-WHF Global Task Force recommendations for use in the diagnosis of MI.