BACKGROUND: Cardiac troponin T measured by a high-sensitivity assay (hs-cTnT) recently proved to be of prognostic value in several populations. The hs-cTnT assay may also improve risk stratification in acute dyspnea. METHODS: We prospectively studied the prognostic value of hs-cTnT in 678 consecutive patients presenting to the emergency department with acute dyspnea. On the basis of conventional cardiac troponin T assay (cTnT) and hs-cTnT assay measurements, patients were divided into 3 categories: (1) neither assay increased (cTnT<0.03 mug/L, hs-cTnT<0.016 mug/L), (2) only hs-cTnT increased>/=0.016 mug/L (cTnT<0.03 mug/L), and (3) both assays increased (cTnT>/=0.03 mug/L, hs-cTnT>/=0.016 mug/L). Moreover, the prognostic value of hs-cTnT was investigated if cTnT was not detectable (<0.01). RESULTS: One hundred seventy-two patients were in the lowest, 282 patients in the middle, and 223 patients in the highest troponin category. Patients in the second and third categories had significantly higher mortality compared to those in the first category (90-day mortality rate 2%, 10%, and 26% in groups 1, 2, and 3, respectively, P<0.001; 1-year mortality rate 9%, 21%, and 39%, P<0.001). Importantly, in patients with undetectable cTnT (n=347, 51%), increased hs-cTnT indicated worse outcome [90-day mortality, odds ratio 4.26 (95% CI 1.19-15.21); 1-year mortality, hazard ratio 2.27 (1.19-4.36), P=0.013], whereas N-terminal pro-brain-type natriuretic peptide (NT-proBNP) was not predictive of short-term outcome. CONCLUSIONS: hs-cTnT is associated with mortality in patients presenting with acute dyspnea. hs-cTnT concentrations provide additional prognostic information to cTnT and NT-proBNP testing in patients with cTnT concentrations below the detection limit. In particular, the hs-cTnT cutoff of 0.016 mug/L enables identification of low-risk patients.