Structural drivers of persistent CK-MB testing in the troponin era and a nationwide monitoring framework for cardiac biomarker stewardship

International guidelines consider CK-MB and myoglobin to be of low or limited value for diagnosing acute myocardial infarction (AMI), but how to target and monitor cardiac biomarker stewardship remains unclear. Using Korean nationwide single-payer claims (2010–2024), we analyzed the earliest claim per patient with acute ischemic heart disease (AIHD) and at least one cardiac biomarker order (CK-MB, myoglobin, or troponin), computing troponin-only ordering rates by AMI status, institution type, region, and department. The troponin-only rate remained between 3% and 4% through 2020 and reached 5.27% in 2024 (15-year average 3.9%). In claims-defined AMI, it was 0.4–0.8% each year and did not change despite guideline updates, compared with 3.8–7.2% in non-AMI AIHD. Tertiary and general hospitals accounted for about 97% of claims; the rate rose from 2.4% to 6.4% in tertiary hospitals but changed little in general hospitals (4.0% in 2010 and 4.7% in 2024). Pooled departmental rates were 3.3% in cardiology, 6.9% in general internal medicine, and 2.6% in emergency medicine. Despite consistent international guidelines, CK-MB co-ordering persisted across all major departments and nearly every claims-defined AMI claim. We identify tertiary hospitals and high-volume departments as priority stewardship targets, and propose the troponin-only ordering rate stratified by institution and department as a transferable population-scale monitoring indicator.