How well do anatomical-based injury severity scores predict health service use in the 12 months after injury?

There is an acknowledged need for valid and reliable injury scores, suitable for use at the population level, which can accurately predict the long-term outcome of injury. The objective was to quantify the extent to which the abbreviated injury severity score (AIS) and the functional capacity index score (FCI) predict use of health services in the 12 months following an injury event. A cohort of injured people (ICD-9-CM 800-995) aged 18 - 64 years was identified from Manitoba hospital discharge abstracts from January 1988 to December 1991. For each member of the cohort whose injuries could be mapped to an abbreviated injury scale unique identifier, a maximum AIS (maxAIS) and a maximum FCI (maxFCI) were obtained. The cohort was linked with hospital discharge abstracts, physicians' claims and deaths from the population registry for the 12 months following injury. Negative binomial regression was used to model the relationships between the severity scores and the three outcome measures, while controlling for potential confounding variables. In total, 20 677 (97%) eligible cases were identified, of which 16 834 (81%) could be assigned a maxAIS and 15 823 (77%) a maxFCI. MaxAIS and maxFCI were significantly associated with total days in hospital following injury, but explained little of the variation in any of the health service use outcome variables (maxAIS, partial pseudo r2 ranging from < 0.001 to 0.041; and maxFCI, partial pseudo r2 ranging from < 0.001 to 0.018). It was concluded that anatomical damage is only partly responsible for long-term injury outcome. Additional variables would need to be included in predictive models of health outcomes of injury before these models could be reliable