The intermountain risk score predicts incremental age-specific long-term survival and life expectancy

Abstract

The Intermountain Risk Score (IMRS) encapsulates the mortality risk information from all components of the complete blood count (CBC) and basic metabolic profile (BMP), along with age. To individualize the IMRS more clearly, this study evaluated whether IMRS weightings for 1-year mortality predict age-specific survival over more than a decade of follow-up. Sex-specific 1-year IMRS values were calculated for general medical patients with CBC and BMP laboratory tests drawn during 1999-2005. The population was divided randomly 60% (N = 71,921, examination sample) and 40% (N = 47,458, validation sample). Age-specific risk thresholds were established, and both survival and life expectancy were compared across low-, moderate-, and high-risk IMRS categories. During 7.3 ± 1.8 years of follow-up (range, 4.5-11.1 years), the average IMRS of decedents was higher than censored in all age/sex strata (all P < 0.001). For examination and validation samples, every age stratum had incrementally lower survival for higher risk IMRS, with hazard ratios of 2.5-8.5 (P < 0.001). Life expectancies were also significantly shorter for higher risk IMRS (all P < 0.001): For example, among 50-59 year-olds, life expectancy was 7.5, 6.8, and 5.9 years for women with low-, moderate-, and high-risk IMRS (with mortality in 5.7%, 16.3%, and 37.0% of patients, respectively). In Men, life expectancy was 7.3, 6.8, and 5.4 for low-, moderate-, and high-risk IMRS (with patients having 7.3%, 19.5%, and 40.0% mortality), respectively. IMRS significantly stratified survival and life expectancy within age-defined subgroups during more than a decade of follow-up. IMRS may be used to stratify age-specific risk of mortality in research, clinical/preventive, and quality improvement applications. A web calculator is located at http://intermountainhealthcare.org/IMRS.