Development and validation of an age-risk score for mortality predication after thermal injury

Background: In burn patients, the risk of mortality typically decreases as children mature, reaches a nadir at age 21, rises linearly thereafter, and levels off in old age. We hypothesized that a single "age-risk score" (AGESCORE), incorporating a cubic functional form, can be used in predictive models for mortality after burns. Methods: Data from 6,395 thermally injured patients admitted to a single burn center between January 1, 1950, and December 31, 1999, were used. Variables included age, total burn size, year of discharge, and survival. AGESCORE was defined as follows: -5(age) + 14(age ²/100) - 7(age³/10,000). Logistic regression verified the cubic functional form of the age-mortality relationship. Models using a general cubic functional form of age, and AGESCORE, were compared for lack of fit. The stability of AGESCORE was assessed over six distinct treatment eras within the 50-year period. AGESCORE was also validated using data from a different burn center. Results: AGESCORE provided an accurate method for modeling mortality in burn patients across different age groups, burn sizes, eras, and burn centers. Conclusion: The benefits of a standardized index of age risk include ease of comparison, reduction of bias, and increased efficiency attributable to statistical parsimony. The applicability of this approach to nonthermal trauma patients remains to be seen.