Implementation of a highly sensitive cardiac troponin I assay: test volumes, positivity rates and interpretation of results.

BACKGROUND: While more sensitive cardiac troponin (cTn) assays may overcome current limitations in diagnosing acute coronary syndrome (ACS), clinicians and laboratorians are concerned about the clinical impact of higher rates of cTn positivity.
METHODS: We collected statistics on test volume and positivity rates before and after the implementation of a more sensitive assay. We divided patients into 6 groups based on their cardiac troponin I (cTnI) results and utilized additional laboratory test results to determine the impact of the new assay. In addition, we assessed the clinical significance of low-positive cTnI results (0.05-0.10 microg/l).
RESULTS: Lowering the diagnostic cutoff from 0.10 to 0.04 microg/l increased the number of positive test results by 44.2% hospital-wide and 114.4% in the emergency department without significantly changing test volume. In some patients, low-positive results were part of the typical rise and fall of cTnI consistent with myocardial damage. Diagnosis was more challenging in patients with consistently low-positive results. Patients in this group were significantly more likely to have impaired renal function than those with cTnI elevations >0.10 microg/l.
CONCLUSIONS: More sensitive cTn assays will increase the number of positive results and allow for earlier detection of cardiac injury while also detecting non-ACS related pathologies.