Sensitivity and specificity of traumatic brain injury diagnosis codes in United States Department of Veterans Affairs administrative data

Objective: To examine the validity of using International Classification of Diseases (ICD) diagnosis codes from United States Department of Veterans Affairs (VA) data to describe prevalence of traumatic brain injury (TBI) among military veterans. Methods: VA clinicians complete a standardized TBI evaluation to determine whether veterans' deployment exposures resulted in TBI. Clinician-confirmed cases and non-cases of TBI were used as recorded on the evaluation as the criterion standard against which to evaluate three series of TBI-related ICD diagnosis codes in national VA datasets. Focusing on codes used within VA, measures of validity were calculated and correlates of discordance examined, including patient characteristics, region and time. Secondarily, it was examined whether TBI codes can differentiate mild from more severe TBI cases. Results: Of 49 962 veterans with completed TBI evaluations, 29 534 (59%) received clinician-confirmed TBI diagnoses. Sensitivity of the VA series of codes was 70%, specificity was 82% and concordance was 75%. Concordance varied by region, but not by patient characteristics or time. Codes were not useful for distinguishing mild TBI. Conclusion: Estimates of TBI prevalence in military veterans are important for national programme development and resource distribution. Estimates derived from ICD diagnosis codes in administrative data should take potential misclassification into account.