Are We Underestimating the Burden of Traumatic Brain Injury? Surveillance of Severe Traumatic Brain Injury Using Centers for Disease Control International Classification of Disease, Ninth Revision, Clinical Modification, Traumatic Brain Injury Codes

BACKGROUND: The epidemiology of traumatic brain injury (TBI) is often studied through the use of International Classification of Disease, ninth revision, clinical modification (ICD-9-CM), diagnosis codes from the Centers for Disease Control and Prevention TBI Surveillance System. Recent studies suggest that these codes may underestimate the burden of TBI because of inaccuracies and low sensitivity. OBJECTIVE: To determine the sensitivity and specificity of ICD-9-CM codes in a severe TBI population. METHODS: We retrospectively reviewed medical records of all hospital admissions including computed tomography of the head at a single center to identify severe blunt TBI patients, their injuries, and the neurosurgical procedures performed. We calculated sensitivity and specificity by comparing ICD-9-CM diagnosis and procedure codes assigned by hospital coders with medical records, the gold standard. RESULTS: In 2008, there were 148 qualifying admissions. These codes were 89% sensitive for the presence of any severe TBI. However, one-fifth of these cases were identified only with a code defining a nonspecific head injury. Next, we studied types of TBI by categories defined by the Centers for Disease Control and Prevention (morbidity groups) and by ICD-9-CM codes for types of injury (any skull fracture, intracranial contusion, intracranial hemorrhage, concussion/loss of consciousness) and found widely varying sensitivity and specificity for both. In general, these codes had higher specificity than sensitivity. Both sensitivity and specificity were > 80% for only 2 categories: any skull fracture and intracranial hemorrhage. In contrast, we found high sensitivity and specificity for neurosurgical procedures (97% and 94%). CONCLUSION: ICD-9-CM codes were sensitive for the presence of any severe TBI, but further classification of specific types of TBI was limited by variable sensitivity/specificity. Use of these codes should be supplemented by other methodology.