Diagnostic parameters of CK-MB and myoglobin related to chest pain duration.

Objective: Cardiac marker sensitivity depends on chest pain duration at the time of sampling. Our objective was to estimate the sensitivity, specificity, and likelihood ratios of early CK-MB and myoglobin assays in patients presenting to the emergency department (ED) with nondiagnostic ECGs, stratified by the duration of ongoing chest pain at the time of ED assessment.

Methods: This was a prospective observational study carried out in 10 US and 2 Canadian EDs. Patients >25 years of age with ongoing chest pain and nondiagnostic ECGs were stratified by pain duration (0-4 h, 4-8 h, 8-12 h, >12 h). CK-MB and myoglobin assays were drawn at T = 0 (ED assessment) and T = 1 hr. Patients were followed for 7-14 days to identify all cases of acute myocardial infarction (AMI). ED test results were correlated with patient outcomes.

Results: Of 5005 eligible patients, 565 had AMI. Pain duration was 0-4 h in 3014 patients, 4-8 h in 961, 8-12 h in 487, and >12 h in 543. Marker sensitivity increased with pain duration, ranging from 28%-77% for CK-MB and 39%-73% for myoglobin. The maximal sensitivity achieved by a T = 0 assay was 73%, and this was in patients with 8-12 or >12 h of ongoing pain. No combination of tests achieved 90% sensitivity in any pain duration strata.

Conclusions: Regardless of chest pain duration, single assays and early serial markers (0+1 hr) do not rule out AMI; therefore, serial assays over longer observation periods are required. Likelihood ratios derived in this study will help physicians who use Bayesian analysis to determine post-test AMI likelihood in patients with chest pain.