The Charlson comorbidity index (CCI) for adjustment of hip fracture mortality in the elderly: analysis of the importance of recording secondary diagnoses

This study evaluates the role of the number of secondary diagnoses for calculating the Charlson comorbidity index (CCI) in risk adjustment of the 90-day mortality rate after hip fracture surgical repair. Comorbidities were selected by reviewing the medical records of 390 patients 50 years of age or older in a teaching hospital in Rio de Janeiro from 1995 to 2000. Logistic regression models were fitted including the variables age, sex, and CCI. The CCI was calculated based on: (1) all patients' comorbidities; (2) only the comorbidity with the highest weight; and (3) a single randomly selected comorbidity. There was a gradient in the prediction of the CCI mortality rate when all comorbidities were used (OR = 6.53; 95%CI: 2.27-18.77, for scores >or= 3). The predictive capacity of the CCI was observed even when it was calculated using only one comorbidity: with the highest weight (OR = 2.83; 95%CI: 1.11-7.22); and randomly selected (OR = 2.90; 95%CI: 1.07-7.81). Using all comorbidities for CCI calculation is important. Severity indices based on a single comorbidity can be useful for risk adjustment procedures.