Frailty index as a predictor of mortality: a systematic review and meta-analysis

Background: two popular operational definitions of frailty, the frailty phenotype and Frailty index (FI), are based on different theories. Although FI was shown to be superior in predicting mortality to the frailty phenotype, no meta-analysis on mortality risk according to FI has been found in the literature. Methods: an electronic systematic literature search was conducted in August 2016 using four databases (Embase, Medline, CINAHL and PsycINFO) for prospective cohort studies published in 2000 or later, examining the mortality risk according to frailty measured by FI. A meta-analysis was performed to synthesise pooled mortality risk estimates. Results: of 2,617 studies identified by the systematic review, 18 cohorts from 19 studies were included. Thirteen cohorts showed hazard ratios (HRs) per 0.01 increase in FI, six cohorts showed HRs per 0.1 increase in FI and two cohorts each showed odds ratios (ORs) per 0.01 and 0.1 increase in FI, respectively. All meta-analyses suggested that higher FI was significantly associated with higher mortality risk (pooled HR per 0.01 FI increase = 1.039, 95% CI = 1.033-1.044, P < 0.001; pooled HR per 0.1 FI increase = 1.282, 95% CI = 1.258-1.307, P < 0.001; pooled OR per 0.01 FI increase = 1.054, 95% CI = 1.040-1.068, P < 0.001; pooled OR per 0.1 FI increase = 1.706, 95% CI = 1.547-1.881, P < 0.001). Meta-regression analysis among 13 cohorts with HR per 0.01 increase in FI showed that the studies with shorter follow-up periods and with lower female proportion were associated with higher mortality risks by FI. Conclusions: this systematic review and meta-analysis was the first to quantitatively demonstrate that frailty measured by the FI is a significant predictor of mortality.