Abstract
BackgroundTroponins (highly sensitive biomarkers of myocardial damage) increase counts of myocardial infarction (MI) in clinical practice, but their impact on trends in admission rates for MI in National statistics is uncertain.MethodsCases coded as MI or other cardiac diagnoses in the Hospital Morbidity Data Collection (MI-HMDC) in Western Australia in 1998 and 2003 were classified using revised criteria for MI developed by an International panel convened by the American Heart Association (AHA criteria) using information on symptoms, ECGs and cardiac biomarkers abstracted from samples of medical notes. Age-sex standardized rates of MI-HMDC were compared with rates of MI based on AHA criteria including troponins (MI-AHA) or traditional biomarkers only (MI-AHAck).ResultsBetween 1998 and 2003, rates of MI-HMDC decreased by 3.5% whereas rates of MI-AHA increased by 17%, a difference largely due to increased false-negative cases in the HMDC associated with marked increased use of troponin tests in cardiac admissions generally, and progressively lower test thresholds. In contrast, rates of MI-AHAck declined by 18%.ConclusionsIncreasing misclassification of MI-AHA by the HMDC may be due to reluctance by clinicians to diagnose MI based on relatively small increases in troponin levels. These influences are likely to continue. Monitoring MI using AHA criteria will require calibration of commercially available troponin tests and agreement on lower diagnostic thresholds for epidemiological studies. Declining rates of MI-AHAck are consistent with long-standing trends in MI in Western Australia, suggesting that neither MI-HMDC nor MI-AHA reflect the true underlying population trends in MI.
Highlights
Troponins increase counts of myocardial infarction (MI) in clinical practice, but their impact on trends in admission rates for MI in National statistics is uncertain
Between 1998 and 2003, episodes of care for MI increased by 11% whilst those for unstable angina pectoris (UAP) decreased by 26%
The prevalence of troponin tests in cases not coded as MI or UAP increased from 33% to 63%
Summary
Troponins (highly sensitive biomarkers of myocardial damage) increase counts of myocardial infarction (MI) in clinical practice, but their impact on trends in admission rates for MI in National statistics is uncertain. Routinely collected mortality and hospital morbidity data are the most commonly used alternative for monitoring trends in MI. While such data have major shortcomings, studies in Finland, Sweden and Western Australia have previously shown reasonable agreement between trends based on registers and administrative data [7,8,9]. The recent widespread introduction into clinical practice of highly sensitive and specific biomarkers of myocardial damage, troponin tests, raises doubts about the reliability of administrative data for monitoring MI. Studies in Perth, Western Australia, and Denmark have shown that declining trends in hospital MI admissions reversed or levelled out since the introduction of troponin tests in 1996 [5,11]
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