Frailty in NHANES: Comparing the frailty index and phenotype.

The two most commonly employed frailty measures are the frailty phenotype and the frailty index. We compared them to examine whether they demonstrated common characteristics of frailty scales, and to examine their association with adverse health measures including disability, self-reported health, and healthcare utilization. The study examined adults aged 50+ (n=4096) from a sequential, cross-sectional sample (2003-2004; 2005-2006), National Health and Nutrition Examination Survey. The frailty phenotype was modified from a previously adapted version and a 46-item frailty index was created following a standard protocol. Both measures demonstrated a right-skewed distribution, higher levels of frailty in women, exponential increase with age and associations with high healthcare utilization and poor self-reported health. More people classified as frail by the modified phenotype had ADL disability (97.8%) compared with the frailty index (56.6%) and similarly for IADL disability (95% vs. 85.6%). The prevalence of frailty was 3.6% using the modified frailty phenotype and 34% using the frailty index. Frailty index scores in those who were classified as robust by the modified phenotype were still significantly associated with poor self-reported health and high healthcare utilization. The frailty index and the modified frailty phenotype each confirmed previously established characteristics of frailty scales. The agreement between frailty and disability was high with each measure, suggesting that frailty is not simply a pre-disability stage. Overall, the frailty index classified more people as frail, and suggested that it may have the ability to discriminate better at the lower to middle end of the frailty continuum.