To verify the clinical impact of different low cut-offs for troponin I/cardiac troponin I (99th percentile to 10% CV) and for myoglobin, in early risk stratification of patients with suspected acute coronary syndrome.
A total of 516 consecutive non-ST-elevation patients admitted to hospital were followed. The first measurement of cardiac markers was performed at the point-of-care in the Emergency Cardiology Department, using Stratus CS. The lowest cardiac troponin I concentration with a CV≤10% (cardiac troponin I concentration=0.07 μg/l) was used to perform an early diagnosis of cardiac damage and to admit non-ST-elevation patients to the Intensive Cardiac Unit. Final diagnosis of acute myocardial infarction was assessed according to European Society of Cardiology and American College of Cardiology diagnostic criteria: cardiac marker follow-up after hospital admission was performed in central laboratory. We retrospectively assessed how the diagnostic accuracy of an early diagnosis of myocardiac damage in the same population might have changed if different lower cardiac troponin I cut-offs had been used upon admitting patients in the Emergency Cardiology Department, independently from the analytical imprecision of the method.
A diagnosis of acute myocardial infarction was performed on 110 (21.3%) of 516 non-ST-elevation-patients admitted to hospital. Seventy (13.6%) patients had cardiac troponin I >0.07 μg/l in the Emergency Cardiology Department (P>0.05). Using lowering cut-off values, the difference between the fraction of patients that was positive compared with the diagnosis according to European Society of Cardiology and American College of Cardiology criteria and had remained statistically significant (P<0.05) up to 0.03 μg/l (99th percentile upper reference limit) was considered (85 patients, 16.5%, n.s.). Relative operating characteristic analysis confirmed that the best clinical cut-off was related to the cardiac troponin I concentration that meets the 99th percentile upper reference limit. The diagnostic accuracy of myoglobin in detecting the minimum cardiac damage was significantly lower, independently from the cut-offs considered.
The diagnostic accuracy in detecting myocardial damage early in the Emergency Cardiology Department improves when the 99th percentile is used as a decisional value of cardiac troponin I; the use of this cut-off makes the measurement of myoglobin unnecessary.