German study compared TnT, TnI, and CK-MB
In a study published in the New England Journal of Medicine, German researchers examined 773 patients with normal troponin levels.1 (See related story, p. 56.)
In patients with acute myocardial infarction (AMI), Troponin T (TnT) was positive in 94% and Troponin I (TnI) was elevated in 100%. At six hours, creatine kinase-MB (CK-MB) was positive in 91%. In the unstable angina patients, TnT was positive in 22% and TnI in 36%, but CK-MB was only elevated in 5% of the unstable angina patients on any test. Among the patients with at least one positive troponin test, only in 58% of those with a positive TnT and 64% with a positive TnI was the test positive on arrival.
Among AMI patients, 51% had a positive TnT on arrival, 66% a positive TnI, and 53% a positive CK-MB. Troponins were elevated in some of the patients with other cardiac diagnoses and pulmonary embolism, but only one patient without disease had a positive Tn. Seven patients with renal failure had positive TnT, but not TnI. CK-MB was elevated in 27 patients with negative troponins and no evidence of cardiac disease.
Follow-up at 30 days revealed 34 cardiac events and 20 deaths. If all TnT tests were negative, the event rate was 1.1%, and if all TnI tests were negative, the event rate was 0.3%. When the EKG was considered, no patients with a normal EKG and a normal TnI test had an event.
Reference1. Hamm CW, Goldmann BU, Heeschen C, et al. Emergency room triage of patients with acute chest pain by means of rapid testing for cardiac troponin T or troponin I. N Engl J Med 1997; 337:1,648-1,653.
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