Identifying the mechanism of missingness for unspecified diabetic retinopathy disease severity in the electronic health record: an IRIS® Registry analysis.

Observational studies of diabetic retinopathy (DR) using electronic health record data often determine disease severity using International Classification of Disease (ICD) codes. We investigated the mechanism of missingness for DR severity based on ICD coding using the American Academy of Ophthalmology IRIS® Registry. We included all patient encounters in the registry with a DR ICD-9 or ICD-10 code between January 1, 2014 and June 30, 2021. Demographic, clinical, and practice-level characteristics were compared between encounters with specified and unspecified disease severity. Practices were divided into quartiles based on the proportion of clinical encounters with unspecified DR severity. Encounters with unspecified disease severity were associated with significantly older patient age, better visual acuity, and lower utilization of ophthalmic procedures. Higher volume practices and retina specialist practices had lower proportions of clinical encounters with unspecified disease severity. Results strongly suggest that DR disease severity related to ICD coding is missing not at random.