Session number: 1018
Abstract title: Case-mix Measures Derived from Self-Report of Diagnoses and Health: the Seattle Index of Comorbidity
Author(s):
VS Fan - VA Puget Sound Health Care System, HSR&D and Department of Medicine
DH Au - VA Puget Sound Health Care System, HSR&D and Department of Medicine
P Heagerty - VA Puget Sound Health Care System, HSR&D and Department of Biostatistics
RA Deyo - VA Puget Sound Health Care System, HSR&D and Department of Medicine
MB McDonell - VA Puget Sound Health Care System, HSR&D
SD Fihn - VA Puget Sound Health Care System, HSR&D and Department of Medicine
Objectives: Self-reported chronic diseases and health status are associated with resource use. However, few data exist regarding their ability to predict mortality or hospitalizations. We sought to determine whether self-reported chronic medical conditions and the SF-36 could be used individually or in combination to assess comorbidity in the outpatient setting.
Methods: We conducted a prospective cohort study using data from patients participating in the Ambulatory Care Quality Improvement Project (ACQUIP) conducted at seven Veterans Affairs (VA) medical centers. We identified 10,947 patients >= 50 years of age enrolled in general internal medicine clinics who returned both a baseline health inventory checklist and the baseline SF-36 who were followed for a mean of 722.5 (sd 84.3) days. The primary outcome was all-cause mortality, with a secondary outcome of hospitalization within the VA system.
Results: Using a Cox proportional hazards model in a development set of 5469 patients, a comorbidity index (Seattle Index of Comorbidity [SIC]) was constructed using information about age, smoking status and 7 of 25 self-reported medical conditions that were associated with increased mortality. In the validation set of 5478 patients, the SIC was predictive of both mortality and hospitalizations within the VA system. A separate model was constructed in which only age and the PCS and MCS scores of the SF-36 were entered to predict mortality. The SF-36 component scores and the SIC had comparable discriminatory ability (AUC for discrimination of death within 2 years 0.71 for both models). When combined, the SIC and SF-36 together had improved discrimination for mortality (AUC=0.74, p-value for difference in AUC < 0.005).
Conclusions: A new outpatient comorbidity score developed using self-identified chronic medical conditions on a baseline health inventory checklist was predictive of 2-year mortality and hospitalization within the VA system in general internal medicine patients.
Impact statement: This study suggests that a brief self-administered questionnaire with 9 items, including 7 chronic medical conditions, age and smoking status can be used to adjust for comorbidity in outpatient studies. Alternatively, if the SF-36 is available, the PCS and MCS might also be used as a general measure of comorbidity.