Survival among hospital in-patients with troponin T elevation below levels defining myocardial infarction.

BACKGROUND Cardiac troponin T (cTnT) has an accepted place in the management of patients presenting with suspected acute coronary syndrome (ACS). Uncertainty remains about the significance and interpretation of elevated cTnT below the cut-off levels defining myocardial infarction (0.1 microg/l). AIM To compare the mortality risks for elevation of cTnT in the ranges 0.01-0.029 microg/l, 0.03-0.099 microg/l and <0.01 microg/l. DESIGN Retrospective record study in three hospitals. METHODS All cTnT measurements with values in the range >0.01-0.099 microg/l analysed during January 2002 were extracted from clinical biochemistry laboratory databases. Following agreed exclusion criteria, 179 patients with cTnT in the range 0.01-0.099 microg/l and 60 patients <0.01 microg/l were selected at random from across the three sites. Six-month follow-up was completed by review of case notes and contact with the patients' GP. RESULTS There was a graded increase in mortality with increasing cTnT, although only achieving statistical significance for patients in the 0.03-0.099 microg/l range. The graded increase in relative risk with cTnT was weaker after adjustment for potential confounding factors DISCUSSION We found a trend for worse survival with increasing cTnT within the range 0.01-0.099 microg/l in unselected patient populations presenting with possible acute coronary syndrome. This suggests that the combined effects of assay imprecision and co-morbidity should be taken into account when interpreting borderline elevation of cTnT. The use of a cut-off based on current standards of assay precision should be used to define the sensitivity of cTnT as biochemical evidence of ischaemic cardiac damage and as an indicator of mortality risk. This level is likely to be between 0.03 and 0.1 microg/l.