Background — Cardiac health services researchers frequently use cohorts derived from administrative hospital discharge abstract data to study the outcomes and treatment of coronary artery disease. However, relatively limited data exist on the accuracy of the coding of cardiac diagnoses in discharge abstract data. The goal of this study was to examine the accuracy of the coding of acute myocardial infarction and other cardiac diagnoses in the Canadian Institute of Health Information hospital discharge abstracts.
Methods — Patients admitted to 58 cardiac care units (CCUs) in Ontario that participated in the Fastrak II Acute Coronary Syndromes registry were linked to CIHI hospital discharge abstracts. The most responsible diagnosis at hospital discharge in the administrative data was compared with the CCU discharge diagnosis in the clinical registry.
Results — A total of 58,816 CCU patients were linked to hospital discharge abstract data. The specificity, sensitivity, and positive predictive value of a most responsible diagnosis of acute myocardial infarction were 92.8%, 88.8%, and 88.5%, respectively. The specificity of CIHI diagnosis codes for arrhythmia, congestive heart failure, unstable angina, and chest pain not yet diagnosed were all at least 93.9%. However, the sensitivity of these CIHI diagnosis codes was no greater than 60.7%. Furthermore, the positive predictive values were no larger than 80.8%.
Conclusion — Myocardial infarction is generally accurately coded in Ontario hospital discharge abstract data. However, other cardiac diagnoses are less reliably coded in discharge abstract data.