Predicting work-related disability and medical cost outcomes: estimating injury severity scores from workers' compensation data.

Purpose: Acute work-related trauma is a leading cause of death and disability among US workers. The research objectives were to assess: (1) the feasibility of estimating Abbreviated Injury Scale-based injury severity scores (ISS) from ICD-9-CM codes available in workers' compensation (WC) medical billing data, (2) whether ISS predicts work-related disability and medical cost outcomes, (3) whether ISS adds value over other injury severity proxies, and (4) whether the utility of ISS differs for an all-injury sample compared with three specific injury samples (amputations, extremity fractures, traumatic brain injury).

Methods: ISS was estimated from ICD-9-CM codes using Stata's user-written -icdpic- program for 208,522 compensable nonfatal WC claims for workers injured in Washington State from 1998 to 2008. The Akaike Information Criterion and R(2) were used to compare severity measures. Competing risks survival analysis was used to evaluate work disability outcomes. Adjusted total medical costs were modeled using linear regression.

Results: Work disability and medical costs increased monotonically with injury severity. For a subset of 4,301 claims linked to the Washington State Trauma Registry (WTR), there was moderate agreement between WC-based ISS and WTR-based ISS. Including ISS together with an early hospitalization indicator resulted in the most informative models; however, early hospitalization is a more downstream measure.

Conclusions: ISS was significantly associated with work disability and medical cost outcomes for work-related injuries. Injury severity should be considered as a potential confounder for occupational injury intervention, program evaluation, or outcome studies, and can be estimated using existing software when ICD-9-CM codes are available.