The new, highly sensitive cardiac troponin T assay finds detectable levels of the biomarker in 25% of adults in the general population who would not be identified by the standard troponin T assay, and that result often correlates with cardiac structural abnormalities, according to large cohort study reported in the Dec. 8 issue of JAMA.
In addition, elevated cardiac troponin T levels identified with the highly sensitive assay also correlate with all-cause and cardiovascular mortality, independently of other risk factors and even in people thought to be at low cardiovascular risk, said Dr. James A. de Lemos of the University of Texas Southwestern Medical Center, Dallas, and his associates.
The highly sensitive assay detects levels of cardiac troponin T that are approximately one-tenth of the levels detectable with the standard assay. Dr. de Lemos and his colleagues examined the results of this assay in a general population cohort of adults aged 30-65 years participating in the Dallas Heart Study. The 3,546 subjects in this random probability sample had detailed cardiovascular profiles, including MRI and electron-beam CT imaging of the heart and aorta, and their mortality was tracked for a median of 6 years.
The prevalence of detectable cardiac troponin T by this highly sensitive assay was 25% in this multiethnic cohort that included a high proportion of blacks and women. In contrast, the standard assay found detectable levels in only 0.7%.
Higher levels of the biomarker on the highly sensitive assay were associated with cardiac structural abnormalities including left ventricular hypertrophy (both wall thickening and dilation) and left ventricular systolic dysfunction, even in subjects who were asymptomatic, had no known CVD, and were classified as low-risk by their Framingham Risk Scores.
"Moreover, higher cardiac troponin T levels demonstrate[d] a graded association with all-cause and cardiovascular mortality, independent of traditional risk factors, renal function, and levels of other biomarkers" such as high-sensitivity C-reactive protein and N-terminal prohormone brain natriuretic peptide, the investigators said (JAMA 2010;304:2503-12).
"Prior studies have described associations between increased troponin levels detected with standard assays and future risk for mortality. Here, we report that these associations extend to much lower troponin levels not detected with assays in current clinical use," they added.
More research is needed to determine whether routine use of the highly sensitive assay would aid in cardiovascular risk assessment in the general population.
In the meantime, the findings have important implications for the use of this assay for diagnosing acute MI in the hospital setting. Given that one-fourth of the general population have "elevated" troponin T on this test, false-positive diagnoses will increase. "It is possible that widespread application of highly sensitive assays without integrating new approaches to discriminate acute injury will expose some patients to unnecessary risk and expense," Dr. de Lemos and his associates noted.
The Dallas Heart Study was supported by the Donald W. Reynolds Foundation and the National Institutes of Health. Assays were provided by Roche Diagnostics. Dr. de Lemos and his associates reported ties to numerous pharmaceutical and device manufacturers.