Coding accuracy of hospital discharge data for elderly survivors of myocardial infarction

OBJECTIVE: To assess the coding accuracy of primary and secondary discharge diagnoses in the Quebec hospital discharge database for elderly persons wi th myocardial infarction (MI). DESIGN: Retrospective chart review in a convenience sample of six Montreal hospitals. The diagnoses listed in the medical chart were compared with tho se listed in the hospital discharge database. For each subject, the Charlso n comorbidity index was calculated twice, once based on the medical chart a nd again based on the hospital discharge database. PATIENTS: Subjects aged 65 years and over who had an MI coded as the primar y discharge diagnosis in the hospital discharge database and who were disch arged alive. MAIN RESULTS: For 234 MI survivors, the positive predictive value (ie, prob ability that a patient with MI reported in the hospital discharge database had an MI diagnosed by the discharging physician) for coding MI was 0.96 (9 5% CI 0.94, 0.98). Comorbid medical conditions and complications of the MI were underreported in the hospital discharge database, which meant that the Charlson index based on the hospital discharge database was an average of 0.71 units lower than the Charlson index based on the medical chart. CONCLUSIONS: When studying survivors of MI by using hospital discharge data bases, the advantages must be weighed against potential drawbacks in the qu ality of the information. Hospital discharge databases are almost as reliab le as medical charts for identifying MI patients, but there is substantial under reporting of comorbid medical conditions.