Background: Quality-of-care and outcomes research rely on proper coding of acute myocardial infarction (MI). Given the under-appreciation of MI in younger patients, as well as other conditions which may mimic MI, our purpose was to determine the extent to which diagnostic coding can discriminate young patients with MI from those who may present with alternate diagnoses that can account for elevated cardiac biomarkers.
Methods: Using clinical and coding data, we identified all patients presenting with a potential first MI (elevated cardiac biomarkers, ICD9 and ICD10 codes) at a young age (women < 50; men < 45 years of age) to two large medical centers over a 16-year period. Diagnosis and type of MI were adjudicated by review of medical records, as defined by the Third Universal Definition of MI.
Results: A total of 4531 patients (1951 women and 2580 men) with suspected MI were included in the analysis. Of those who ruled-in for MI (N=1579), only 1065 (67%) were accurately identified by diagnosis codes. Of 2952 patients who ruled-out for MI, 814 (27.5%) were falsely coded for MI. These patients had alternative explanations for their presentation, including: severe renal dysfunction (20.3%), myocarditis (13.7%), pulmonary embolism (5.4%), rhabdomyolysis/myositis (2.1%), and chest wall trauma (2.1%). The overall sensitivity of diagnosis codes was 67% and specificity was 72%.
Conclusions: Misclassifications in acute MI coding are highly prevalent in young patients with suspected acute coronary syndrome. Diagnostic codes had a modest sensitivity and specificity for diagnosing acute MI in young patients. False positive coding for MI among young individuals was largely due to confounding presentations, such as myocarditis, that increase cardiac biomarkers.