Reference values for cardiac troponins I and T in a goal-oriented concept of health: cardiac marker values in a series of outpatients without acute coronary syndromes.

BACKGROUND: Cardiac troponins are part of the new definition of acute myocardial infarction (AMI) by the European Society of Cardiology and the American College of Cardiology (ESC/ACC). In the new guidelines, it was suggested to establish reference values for cardiac troponins to calculate the 0.99 quantile (Q99) as cutoff for AMI diagnosis.

PATIENTS AND METHODS: We run a prospective series of troponin measurements in unselected outpatients who had no suspicion of cardiac ischemia. The selection of patients as reference population is based on a "goal-oriented concept of health". One hundred and ninety-five patients agreed that 10-ml additional blood was drawn at the occasion of the venous puncture done routinely in the evaluation of their case. Cardiac troponin I was measured using a point of care (POCT) device (Stratus CS, DadeBehring, TNI-PO). Additionally, heparin-plasma was obtained and immediately deep-frozen to -80 degrees C for later batch measurement of cardiac troponin T (Elecsys 2010, Roche Diagnostics, TnT) and troponin I (Centaur, Bayer, TnI-CL).

RESULTS: The Q99 values were 0.14 microg/l for TnI-PO, 0.023 microg/l for TnT and 0.07 microg/l for TnI-CL in patients with creatinine levels below 1.5 mg/dl. These values lay above those obtained from people at good health for reference study purposes. On the level of our cutoffs, CVs were 7.5%, 6.4% and 23.7% for TnI-PO, TnT and TnI-CL, respectively.

CONCLUSIONS: Only the TnI-PO and TnT tests fulfilled the imprecision criteria in our study. TnI-PO values between 0.10 and 0.14 microg/l and TnT values between 0.01 and 0.03 microg/l have to be interpreted carefully. Patients presenting with chest pain will be possibly true positives, but patients without chest pain and nondiagnostic ECGs should be subjected to repetitive troponin measurements and further noninvasive investigation and maybe not directly sent to the cardiac catheter laboratory.