Association between Body Composition and Frailty among Prevalent Hemodialysis Patients: A US Renal Data System Special Study

Studies of frailty among patients on hemodialysis have relied on definitions that substitute self-reported functioning for measures of physical performance and omit weight loss or substitute alternate criteria. We examined the association between body composition and a definition of frailty that includes measured physical performance and weight loss in a cross-sectional analysis of 638 adult patients receiving maintenance hemodialysis at 14 centers. Frailty was defined as having three of following characteristics: weight loss, weakness, exhaustion, low physical activity, and slow gait speed. We performed logistic regression with body mass index (BMI) and bioelectrical impedance spectroscopy (BIS)-derived estimates of intracellular water (ICW), fat mass, and extracellular water (ECW) as the main predictors, and age, sex, race, and comorbidity as covariates. Overall, 30% of participants were frail. Older age (odds ratio [OR], 1.31 per 10 years; 95% confidence interval [95% CI], 1.14 to 1.50), diabetes (OR, 1.65; 95% CI, 1.13 to 2.40), higher fat mass (OR, 1.18; 95% CI, 1.02 to 1.37), and higher ECW (OR, 1.33; 95% CI, 1.20 to 1.47) associated with higher odds of frailty. Higher ICW associated with lower odds of frailty (OR, 0.80 per kg; 95% CI, 0.73 to 0.87). The addition of BMI data did not change the area under the receiver operating characteristics curve (AUC; AUC=0.66 versus 0.66; P=0.71), but the addition of BIS data did change the AUC (AUC=0.72; P<0.001). Thus, individual components of body composition but not BMI associate strongly with frailty in this cohort of patients receiving hemodialysis.Patients on dialysis frequently experience protein energy wasting or loss of protein mass and energy stores, which is likely multifactorial.¹ It has recently been appreciated that the same disorders that underlie protein energy wasting as well as muscle wasting itself are also commonly associated with frailty.^2–4 Although frailty is generally considered to be a geriatric syndrome, individuals with chronic diseases, such as CKD, may be at risk for premature frailty.^5,6 In fact, as many as two thirds to three quarters of patients new to dialysis may be frail by definitions that rely on patient self-report of physical functioning and omit weight loss or substitute alternate criteria for wasting (6,⁷

Table 1.

Definitions of frailty adapted from the Cardiovascular Health Study definition

Components of Frailty	USRDS DMMS Wave 2 (Incident Dialysis)6	CDS (Incident Dialysis)7	REXDP (Prevalent Hemodialysis)8	NHANES (CKD)9	Seattle Kidney Study (CKD Stages 1–4)28
Slowness/weakness	Rand-36 Physical Function Scale score<75	SF-12 Physical Function score<75	Slowness: gait speed over 6 m using cutpoints that correspond to the same speed as the cutpoints from the 15-ft walk in the CHS	Slowness: gait speed over 8 ft with lowest quintile adjusted for sex	Slowness: walking pace assessed over a 4-m course using cutpoints that correspond to the same speed as the cutpoints from the 15-ft walk in the CHS
	The following items are about activities that you might do during a typical day: does your health now limit you in these activities? If so, how much?		Weakness: patients were asked to stand up and sit down five times; the time for the slowest quartile of the SPPB chair stand based on community-dwelling elderly cohorts was used to define frailty	Weakness: based on self-report and defined as present if participants answered some difficulty, much difficulty, or unable to do when asked how much difficulty they have lifting or carrying something as heavy as 10 lbs (like a sack of potatoes or rice)	Weakness: Grip strength using the same absolute cutoffs as in the CHS
	Vigorous activities, such as running, lifting heavy objects, or participating in strenuous sports
	Moderate activities, such as moving a table, pushing a vacuum cleaner, bowling, or playing golf
	Lifting or carrying groceries
	Climbing several flights of stairs
	Climbing one flight of stairs
	Bending, kneeling, or stooping
	Walking more than 1 mi
	Walking several blocks
	Walking 1 block
	Bathing or dressing yourself
Poor endurance/exhaustion	Rand-36 Vitality Scale score<55	SF-12 Vitality score<55	SF-36 Vitality score<55	Defined as present if participants answered some difficulty, much difficulty, or unable to do when asked how much difficulty they have walking from one room to the other on the same level	SF-36 Vitality score<37.5
	How much of the time during the last 30 days?
	Did you feel worn out?
	Did you feel tired?
	Did you have a lot of energy?
	Did you feel full of pep?
Physical inactivity	How often do you exercise (do physical activity during your leisure time)?	Lowest quintile based on age- and sex-specific population norms for the Human Activity Profile	Patients who reported no activity beyond self-care and activities required for living were considered inactive	Compared with most (men/women) your age, would you say that you are more active, less active, or about the same?	Self-reported exercise less than one time per week
	Daily or almost daily			Patients answering less active were classified as inactive
	Four to five times a week
	Two to three times a week
	About one time a week
	Less than one time a week
	Almost never or never
	Patients answering almost never or never were classified as inactive
Unintentional weight loss or shrinkage	Undernourished or cachectic (malnourished) as assessed by data abstractor	Not included	BMI≤18.5 kg/m2	BMI≤18.5 kg/m2	Self-reported ≥10-lb unintentional weight loss in past 6 months

Open in a separate windowSee ref² for Cardiovascular Health Study. USRDS, US Renal Data System; DMMS, Dialysis Morbidity and Mortality Study; CDS, Comprehensive Dialysis Study; REXDP, Renal Exercise Demonstration Project; NHANES, National Health and Nutrition Examination Survey; CHS, Cardiovascular Health Study; SPPB, short physical performance battery.Low Quételet’s (body mass) index (BMI), expressed in kilograms of body weight divided by height squared, has been substituted for the weight loss criterion of the frailty construct in several studies.^8,9 However, BMI is a nonspecific metric of body composition, because the body weight component could reflect adipose tissue or intracellular (muscle) or extracellular (edema) water. The most commonly used definition of frailty, which includes direct measures of gait speed and grip strength (rather than self-reported functioning) as well as weight loss, exhaustion, and level of physical activity,² has only recently been applied in an ESRD population,¹⁰ and the association between frailty and body composition has not been examined systematically in this population.¹¹In this investigation, we sought to determine the extent to which body composition was associated with frailty in a prevalent hemodialysis cohort. We hypothesized that intracellular water (ICW) estimated by bioelectrical impedance spectroscopy (BIS) would be inversely associated and fat mass would be directly associated with frailty in a cohort of prevalent dialysis patients but that BMI would not be associated.