Date Published: November 28, 2016
Publisher: Springer International Publishing
Author(s): Emiel O. Hoogendijk, Olga Theou, Kenneth Rockwood, Bregje D. Onwuteaka-Philipsen, Dorly J. H. Deeg, Martijn Huisman.
Frailty is a state of increased vulnerability to adverse outcomes. The frailty index (FI), defined by the deficit accumulation approach, is a sensitive instrument to measure levels of frailty, and therefore important for longitudinal studies of aging.
To develop an FI in the Longitudinal Aging Study Amsterdam (LASA), and to examine the predictive validity of this FI for 19-year mortality.
LASA is an ongoing study among Dutch older adults, based on a nationally representative sample. A 32-item FI (LASA–FI) was developed at the second LASA measurement wave (1995–1996) among 2218 people aged 57–88 years. An FI score between 0 and 1 was calculated for each individual. The LASA–FI included health deficits from the physical, mental and cognitive domain and can be constructed for most LASA measurement waves. Associations with 19-year mortality were assessed using Kaplan–Meier curves and Cox proportional hazards models.
The mean LASA–FI score was 0.19 (SD = 0.12), with a 99% upper limit of 0.53. Scores were higher in women than men (women = 0.20, SD = 0.13 vs. men = 0.17, SD = 0.11, p < 0.001). The average age-related increase in the log-transformed LASA–FI score was 3.5% per year. In a model adjusted for age and sex, the FI score was significantly associated with 19-year all-cause mortality (HR per 0.01 = 1.03, 95% CI 1.03–1.04, p < 0.001). The key characteristics of the LASA–FI were in line with findings from previous FI studies in population-based samples of older people. The LASA–FI score was associated with mortality and may serve as an internal and external reference value.
Frailty is a state of increased vulnerability to adverse outcomes, such as falls, functional decline, hospitalization and death . As the clinical importance of the concept of frailty is increasingly recognized, it is of major importance to identify frail older adults . Many operational definitions of frailty exist . One of the most widely used is the deficit accumulation approach, also known as the frailty index (FI). It involves the accumulation of diseases, symptoms, signs, disabilities or any deficiency in health with age, based on the idea that a greater number of health deficits indicate higher frailty . Although health deficits increase with age, the FI characterizes age-related decline in health more efficiently than does chronological age . Moreover, the FI has been shown to be a better predictor of adverse outcomes than chronological age  and even some other indices of biological age .
We were able to calculate the LASA–FI for 2218 people out of 2302 available respondents (96.4%). Of the 2218 people in the analytic sample, 2092 (94.3%) had no missing values on the 32 items of the LASA–FI, 103 had only 1 missing item (4.6%), and 23 had 2 to 6 missing items (0.1%). Figure 1 shows the distribution of the LASA–FI, which was skewed to the right.Fig. 1Distribution of the frailty index at baseline (N = 2218)
In this study, we successfully constructed an FI in LASA. We described its characteristics and validated the LASA–FI for 19-year all-cause mortality. The key characteristics of the LASA–FI are consistent with findings from previous studies in population-based samples of older adults: The distribution of the LASA–FI is skewed to the right, the LASA–FI score increases with chronological age, and the average LASA–FI scores are higher in women than in men [6, 8]. Also, the 99% upper limit was below 0.7, as in previous studies [8, 24]. In the current study, the average rate of deficit accumulation with age was 0.035, which was comparable to other longitudinal studies in community-based samples (mean rate of 0.029) .