BACKGROUND: High-sensitivity cardiac troponin assays will augment the frequency of increased results, making important the determination of reference change values to distinguish acute from chronic increases. We assessed short- and long-term biological variability of cardiac troponin T (cTnT) in healthy subjects with a novel high-sensitivity (hs) assay. METHODS: We collected blood from 20 healthy volunteers at 5 time points for short-term study and biweekly at 4 times from the same volunteers for long-term study. We analyzed serum samples in duplicate with a hscTnT assay on the Roche Modular E170 and computed reference change values (RCVs) for analytical, intraindividual, interindividual, and total change values (CVA, CVI , CVG, and CVT, respectively) and the index of individuality (II). We calculated RCVs by using a log-normal approach, owing to the skewed results of the data. RESULTS: Short- and long-term CVA values were 53.5% and 98%. CV I and CVG were 48.2% and 85.9%, respectively, for short-term studies and 94% and 94% for long-term studies. Mean -values for the within-day study were 58% and -57.5%, and between-day mean δ values were 103.4% and -87%.Within- and between- day IIs were 0.8 and 0.14, respectively. CONCLUSIONS: The biological variation demonstrated with the hscTnT assay is higher than prior data for cardiac troponin I. This may be attributed to differences in biology or assay imprecision at low concentrations. A short-term change (RCV log normal) of 85% and a long-term change of 315% is necessary to define a changing pattern.