Accuracy of the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) as a research tool for identification of patients with uveitis and scleritis.

PURPOSE

To report on the accuracy of the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes for identifying patients with polymyalgia rheumatica (PMR) and concurrent noninfectious inflammatory ocular conditions in a large healthcare organization database.

METHODS

Queries for patients with PMR and uveitis or scleritis were executed in two general teaching hospitals' databases. Patients with ocular infections or other rheumatologic conditions were excluded. Patients with PMR and ocular inflammation were identified, and medical records were reviewed to confirm accuracy.

RESULTS

The query identified 10,697 patients with the ICD-9-CM code for PMR and 4154 patients with the codes for noninfectious inflammatory ocular conditions. The number of patients with both PMR and noninfectious uveitis or scleritis by ICD-9-CM codes was 66. On detailed review of the charts of these 66 patients, 31 (47%) had a clinical diagnosis of PMR, 43 (65%) had noninfectious uveitis or scleritis, and only 20 (30%) had PMR with concurrent noninfectious uveitis or scleritis confirmed based on clinical notes.

CONCLUSIONS

While the use of ICD-9-CM codes has been validated for medical research of common diseases, our results suggest that ICD-9-CM codes may be of limited value for epidemiological investigations of diseases which can be more difficult to diagnose. The ICD-9-CM codes for rarer diseases (PMR, uveitis and scleritis) did not reflect the true clinical problem in a large proportion of our patients. This is particularly true when coding is performed by physicians outside the area of specialty of the diagnosis.