Capture rates of comorbidity measures at inpatient rehabilitation facilities after a stroke or brain injury.

Background: Comorbidity indices have been used to represent the overall medical complexity of patient populations in clinical research; however, it is not known how well they capture the comorbidities of patients with a stroke or brain injury admitted to inpatient rehabilitation facilities (IRFs).

Objective: To determine how well commonly used comorbidity indices capture the comorbidities of patients admitted to IRFs after a stroke or brain injury.

Design: Cross-sectional, retrospective study.

Setting: IRFs nationwide.

Participants: Adults from four impairment groups: (1) hemorrhagic stroke, (2) ischemic stroke, (3) nontraumatic brain injury (NTBI), and (4) traumatic brain injury (TBI).

Main Outcome Measures: International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) codes were extracted from the Uniform Data System for Medical Rehabilitation (UDSMR) for IRF discharges from October 1, 2015 to December 31, 2017. The percentage of discharges captured by Deyo-Charlson, Elixhauser, and Centers for Medicare and Medicaid Services (CMS) tiers was determined, as was the percentage of comorbidities captured. These measures were also compared with respect to their ability to capture chronic medical complexity by examining the percentage of codes captured after removal of codes deemed to represent hospital complications or sequela of the admission diagnosis.

Results: The percentage of discharges without at least one ICD-10-CM code captured by any index ranged from 0.3%-3.8%. The percentage of comorbidities with a prevalence exceeding 1% captured by at least one index ranged from 37.1%-43.6%. Chronic comorbidities were most likely to be captured by Elixhauser (40.7%-44.4%), followed by Deyo-Charlson (7.8%-9.6%), then CMS tiers (4.5%-6.9%). Existing comorbidity measures capture most IRF discharges related to a brain injury or stroke, whereas most medical comorbidities escape representation. Several common, functionally relevant diagnoses were not captured.

Conclusion: The use of comorbidity indices in the IRF neurologic injury population should account for the fact that these measures miss several common, important comorbidities.