Validity of Nonspecific Stroke Location ICD-10 Subcodes: A Descriptive Study

Most ischemic stroke hospitalizations coded with nonspecific/unspecified ICD-10 vascular region subcodes had imaging-confirmed infarcts in specific vascular regions. These strokes tended to have a lower NIHSS and were overrepresented by posterior circulation lesions. The modest variance explained in the use of nonspecific/unspecified codes indicates that much of the coding is influenced by random variation or unmeasured factors. Future studies in other healthcare systems are needed to verify these findings and evaluate for other predictors. Researchers using these subcodes should recognize the limitations and incorporate sensitivity analyses to evaluate potential bias in results.