Validation of an International Classification of Disease, 10th revision coding adaptation for the Charlson Comorbidity Index in United States healthcare claims data

Purpose An International Classification of Disease (ICD‐10) Charlson Comorbidity Index (CCI) adaptation had not been previously developed and validated for United States (US) healthcare claims data. Many researchers use the Canadian adaption by Quan et al (2005), not validated in US data. We sought to evaluate the predictive validity of a US ICD‐10 CCI adaptation in US claims and compare it with the Canadian standard. Methods Diverse patient cohorts (rheumatoid arthritis, hip/knee replacement, lumbar spine surgery, acute myocardial infarction [AMI], stroke, pneumonia) in the IBM® MarketScan® Research Databases were linked with the IBM MarketScan Mortality file. Predictive performance was measured using c‐statistics for binary outcomes (1‐year and postoperative mortality, in‐hospital complications) and root mean square prediction error (RMSE) for continuous outcomes (1‐year all‐cause medical costs, index hospitalization costs, length of stay [LOS]), after adjusting for age and sex. C‐statistics were compared by the method of DeLong and colleagues (1988); RMSEs, by resampling. Results C‐statistics were generally high (≥ ~ 0.8) for mortality but lower for in‐hospital complications (~0.6–0.7). RMSEs for costs and hospitalization LOS were relatively large and comparable to standard deviations. Results were similar overall between the US and Canadian adaptations, with relative differences typically