Measuring medical complexity during inpatient rehabilitation after traumatic brain injury

Objective: To compare the performance of 3 severity of illness (SOI) indices-the Comprehensive Severity Index (CSI), All Patient Refined Diagnosis Related Groups Severity of Illness, case-mix group (CMG)-and 5 well-known neurologic parameters, as measures of medical complexity. Design: Retrospective chart review. Setting: Inpatient rehabilitation center within a level I trauma center. Participants: Consecutive traumatic brain injury (TBI) admissions (N=212). Intervention: Acute inpatient TBI rehabilitation. CSI and neurologic parameters were scored by chart extraction. SOI was based on diagnosis codes by using 3M PC Grouper software, version 15. Main Outcome Measures: Adjusted R-2 was used to predict rehabilitation charges as a proxy of medical complexity. Results: The highest adjusted R-2 values for single variables predicting charges were: CMG .349, CSI .293, duration of post-traumatic amnesia .260. Adjusted R-2 values for the CMG combined with the CSI, 5 neurologic parameters, and SOI to predict charges were .446, .431, and .365, respectively. Conclusions: The CMG was the best single predictor of rehabilitation charges for TBI. Predictive ability was better when the CMG was combined with the CSI or a combination of the 5 neurologic parameters. A severity index based on objective clinical findings rather than diagnostic codes may have distinct advantages for rehabilitation outcome studies and reimbursement methodology.