Study objective: We evaluate associations between pairs of discordant cardiac biomarkers (positive MB band of creatine kinase [CKMB] with negative creatine kinase, positive CKMB with negative cardiac troponin, and positive troponin with negative CKMB) and the presence of acute coronary syndromes in emergency department (ED) chest pain patients.
Methods: This was a secondary analysis of a prospective registry. Data were obtained from the multicenter Internet Tracking Registry of Acute Coronary Syndromes, which included 17,713 ED visits for possible acute coronary syndrome between June 1999 and August 2001. First visits and first ED cardiac biomarker results from the 9 sites, 8 in the United States and 1 in Singapore, were included. Subjects were excluded for incomplete information or an initial ECG consistent with ST-segment elevation myocardial infarction. Acute coronary syndrome was defined by diagnosis-related group code indicating myocardial infarction, positive invasive or noninvasive diagnostic testing, revascularization, or death during hospitalization or within 30 days.
Results: Of 8,769 eligible patients, 1,614 (18.4%) had acute coronary syndrome. The CKMB and cardiac troponin results were discordant in 7% of patients (CKMB+/cardiac troponin-, 4.9%, CKMB-/cardiac troponin+ 2.1%), whereas increased CKMB with normal creatine kinase levels occurred in 239 (3.1%) patients. The unadjusted odds ratios with 95% confidence intervals for acute coronary syndrome in patients with and without discordant markers were: CKMB+/CK- 5.7 (4.4-7.4), CKMB+/CK+ 4.4 (3.6-5.2), CKMB-/cTn+ 4.8 (3.4-6.8), CKMB+/cTn- 2.2 (1.7-2.8), CKMB+/cTn+ 26.6 (18.0-39.3). For the group with cardiac troponin, the reference category was negative troponin and negative CKMB; for the group with creatine kinase, the reference category was negative CKMB but either a positive or negative creatine kinase.
Conclusion: Among the spectrum of ED patients with chest pain, an increased CKMB level with a normal creatine kinase level identifies patients at increased risk for acute coronary syndrome. Similarly, an increased troponin level regardless of CKMB level and an increased CKMB level regardless of troponin level identify patients at higher risk for acute coronary syndrome than those with uniformly normal cardiac biomarker levels. Our data suggest that discordant cardiac biomarkers may identify patients at increased risk for acute coronary syndrome.