Developing and Evaluating a Laboratory-Based Frailty Index for the Prediction of Long-Term Health Outcomes in...

We aimed to construct and evaluate the first laboratory-based frailty index (FI-Lab) for predicting adverse outcomes in systemic lupus erythematosus (SLE) and to compare its predictive ability to that of an existing clinical FI.

We used data from a single-center prospective cohort of adult patients with SLE whose baseline visit occurred between 2010 and 2019. A 30-item FI-Lab was constructed by adapting an existing list of FI-Lab variables. Cox proportional hazards regression examined the association between baseline FI-Lab scores and all-cause mortality, whereas negative binomial regression evaluated the association with organ damage accrual. We compared the performance of multivariable models containing the FI-Lab and/or Systemic Lupus International Collaborating Clinics FI as predictor variables using Akaike information criterion, Harrell's C-statistic, and pseudo-R² values.

Among 283 patients (89% women, mean age 47.7 years), 97 were classified as frail at baseline (FI-Lab >0.21). Frail individuals had increased mortality risk (hazard ratio 3.71, 95% confidence interval [CI] 1.82-7.54) and a higher rate of organ damage accrual during follow-up (incidence rate ratio 2.26; 95% CI 1.59-3.22) compared to nonfrail patients. The FI-Lab remained significantly associated with mortality risk after multivariable adjustment. Although both indices were significant baseline predictors of organ damage accrual during follow-up, the multivariable model containing both FIs outperformed models containing either index alone.

An FI constructed exclusively from routinely collected laboratory variables can measure frailty and predict adverse outcomes in SLE. It may serve as a convenient screening tool to detect subclinical frailty and promote early risk mitigation in this population.