SEARCHING FOR AN IMPROVED CLINICAL COMORBIDITY INDEX FOR USE WITH ICD-9-CM ADMINISTRATIVE DATA

We studied approaches to comorbidity risk adjustment by comparing two ICD-9-CM adaptations (Deyo, Dartmouth-Manitoba) of the Charlson comorb idity index applied to Massachusetts coronary artery bypass surgery da ta. We also developed a new comorbidity index by assigning study-speci fic weights to the original Charlson comorbidity variables. The 2 ICD9 -CM coding adaptations assigned identical Charlson comorbidity scores to 90% of cases, and specific comorbidities were largely found in the same cases (kappa values of 0.72-1.0 for 15 of 16 comorbidities). Mean while, the study-specific comorbidity index identified a 10% subset of patients with 15% mortality, whereas the 5% highest risk patients acc ording to the Charlson index had only 8% mortality (p = 0.01). A model using the new index to predict mortality had better validated perform ance than a model based on the original Charlson index (c = 0.74 vs. 0 .70). Thus, in our population, the ICD-9-CM adaptation used to create the Charlson score mattered little, but using study-specific weights w ith the Charlson variables substantially improved the power of these d ata to predict mortality.