Accuracy of Diagnostic Coding for Sarcoidosis in Electronic Databases: A Population-Based Study

Epidemiologic study of sarcoidosis utilizing electronic databases has been increasingly popular. However, the accuracy of diagnostic codes for sarcoidosis is unknown.

The medical record-linkage system of the Rochester Epidemiology Project was searched to identify all potential adult cases of sarcoidosis between January 1, 1995 and December 31, 2013 in Olmsted County, Minnesota, using the International Classification of Diseases, Ninth Revision (ICD-9) code 135 (sarcoidosis). Complete medical records of those potential cases were individually reviewed. The diagnosis of sarcoidosis was confirmed by the presence of non-caseating granuloma on histopathology, radiographic findings of intrathoracic sarcoidosis, and compatible clinical presentations. Positive predictive value (PPV) was estimated as the number of patients verified to have sarcoidosis divided by the number of patients with a diagnostic code for sarcoidosis.

The study cohort included 366 patients with at least one code for sarcoidosis. Of these, 224 cases of confirmed sarcoidosis were identified, resulting in PPV of 61.2% (95% CI 56.0-66.2%). A total of 268 patients in the database had a code for sarcoidosis on least two occasions separated by at least 30 days. Of these, there were 205 cases of confirmed sarcoidosis. The PPV for having the code at least twice was 76.5% (95% CI 71.0-81.4%).

The PPV of ICD-9 code for sarcoidosis is relatively low and, thus, further verification is required for studies using electronic databases.