Coding of acute myocardial infarction. Clinical and policy implications

Abstract

Study objective: To evaluate the appropriateness of diagnostic coding of acute myocardial infarction across teaching and nonteaching hospitals.

Design: Retrospective review of a random sample of medical records to find evidence of the occurrence and active treatment of acute myocardial infarction during the admission.

Setting: Five tertiary teaching, five other teaching, and five nonteaching hospitals in metropolitan Boston.

Cases: Random sample of hospital admissions assigned a discharge diagnosis of acute myocardial infarction between October 1984 and September 1985.

Measurement and main results: Of the 1003 cases reviewed, 260 did not meet the clinical criteria for acute myocardial infarction. At tertiary hospitals, 175 (41.7%) failed to qualify, compared with 25 (9.1%) at nonteaching facilities. In a large fraction of the disqualified cases, the patients had been admitted to exclude the diagnosis of acute myocardial infarction; although explicitly "ruled out," an acute myocardial infarction code was assigned. Sixty-six cases from teaching hospitals did not qualify because the patient had been admitted only for coronary angiography after an uneventful postmyocardial infarction course. Almost one-third of these patients had had their infarcts from 5 to 8 weeks before the angiography admission.

Conclusions: Cases with an inappropriate discharge diagnosis of acute myocardial infarction may be concentrated in teaching hospitals. This finding could have implications for Medicare's diagnosis-related group payment system and governmental and other research efforts that use these data for such purposes as drawing inferences about the quality of hospital care.