Accuracy of Mild Traumatic Brain Injury Case Ascertainment Using ICD‐9 Codes

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Abstract
Objectives: To determine the accuracy of mild traumatic brain injury (TBI) case ascertainment using International Classification of Diseases, 9th Revision, Clinical Modification (ICD‐9‐CM) codes proposed by the Centers for Disease Control and Prevention (CDC) in a 2003 Report to Congress. Methods: This was a prospective cohort study of all patients presenting to an urban academic emergency department (ED) over six months in 2003. A real‐time clinical assessment of mild TBI was compared with the ICD‐9 codes assigned after ED or hospital discharge for a determination of sensitivity and specificity. Results: Of the 35,096 patients presenting to the ED, 516 had clinically defined mild TBI and 1,000 were assigned one or more of the mild TBI ICD‐9 codes proposed by the CDC. The sensitivity of these codes was 45.9% (95% confidence interval [95% CI] = 41.3% to 50.2%) with a specificity of 97.8% (95% CI = 97.6% to 97.9%). Conclusions: The identification of mild TBI patients using retrospectively assigned ICD‐9 codes appears to be inaccurate. These codes are associated with a significant number of false‐positive and false‐negative code assignments. Mild TBI incidence and prevalence estimates using these codes should be interpreted with caution. ICD‐9 codes should not replace a clinical assessment for mild TBI when accurate case ascertainment is required.
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