Evaluating the properties of a frailty index and its association with mortality risk among patients with systemic lupus erythematosus

Objective: To evaluate the properties of a frailty index (FI), constructed using data from the Systemic Lupus International Collaborating Clinics (SLICC) inception cohort, as a novel health measure in SLE. Methods: For this secondary analysis, the baseline visit was defined as the first study visit at which both organ damage (SLICC/ACR Damage Index [SDI]) and health-related quality of life (Short-Form 36 [SF-36]) were assessed. The SLICC-FI was constructed using baseline data. The SLICC-FI comprises 48 health deficits, including items related to organ damage, disease activity, comorbidities, and functional status. Content, construct, and criterion validity of the SLICC-FI were assessed. Multivariable Cox regression was used to estimate the association between baseline SLICC-FI values and mortality risk, adjusting for demographic and clinical factors. Results: The 1683 SLE patients in the baseline dataset were 89% female with mean (SD) age 35.7 (13.4) years and mean (SD) disease duration 18.8 (15.7) months. At baseline, the mean (SD) SLICC-FI score was 0.17 (0.08) with a range from 0 to 0.51. Baseline SLICC-FI values exhibited the expected measurement properties and were weakly correlated with baseline SDI scores (r=0.262; p<0.0001). Higher baseline SLICC-FI values (per 0.05 increment) were associated with increased mortality risk (Hazard Ratio 1.59; 95%CI 1.35-1.87), after adjusting for age, sex, steroid use, ethnicity/region, and baseline SDI scores. Conclusion: The SLICC-FI demonstrates internal validity as a health measure in SLE and predicts future mortality risk. The SLICC-FI is potentially valuable for quantifying vulnerability among patients with SLE, and adds to existing prognostic scores.