Aberrant body composition, notably muscle and protein-energy wasting, and elevated levels of adiposity, are common characteristics of chronic kidney disease (CKD). Malnutrition, reductions in physical function, and quality of life are negatively affected by abnormal body composition; in addition, there is an association between abnormal body composition and increased risk for adverse clinical outcomes and mortality. Estimates are that 9% to 30% of nondialysis dependent CKD (NDD-CKD) patients are “muscle wasted,” with prevalence higher in more advanced stages.
Obesity, a major factor for cardiovascular disease, is also a risk factor for CKD as well as for more rapid disease progression. There is an association between higher pretransplant muscle mass and increased post-transplant graft and patient survival. An increasing number of transplant recipients are obese; >30% of renal transplant recipients are classified as obese. Obese kidney transplant recipients often have worse short-term outcomes, including the risk of delayed graft function and wound complications.
Routine measurement of body composition relies on the use of body mass index (BMI), calculated using body mass and height. However, according to Thomas J. Wilkinson, PhD, and colleagues, crude BMI phenotyping has limitations in CKD. BMI does not distinguish low muscle mass from adiposity, potentially masking “sarcopenic obesity.”
There is no consensus on the most appropriate method to estimate body composition in patients with CKD. Recent recommendations call for anthropometric estimates and algorithms as adequate alternatives to commonly utilized methods that are limited by accessibility, cost, and the need for trained personnel. The Hume formula has been deemed superior compared with dual-energy X-ray absorptiometry (DXA) and computed tomography imaging. The Hume formula was developed in 1966 to estimate lean mass (LM). The sex-specific formulas require age, sex, height, and body mass (BM).
Male: LM = (0.32810 ★ BM[kg]
) + (0.33929 ★ height [cm]) – 29.5336
Female: LM = (0.29569 ★ BM [kg]) + (0.41813 ★ height [cm]) – 43.2933
The researchers conducted a study to examine the validity of the Hume equation as an estimate of body composition against a reference DXA measurement in a cohort of patients with NDD-CKD and renal transplant recipients. The study also assessed the association between bioelectrical impedance analysis (BIA) and DXA in the two patient groups. The researchers tested the hypothesis that both the Hume equation and BIA would be good estimates of body composition and could offer simple, accessible, and accurate assessments of body composition in clinical practice. Results of the study were reported in the Journal of Renal Nutrition [2019;29(1):16-23].
A total of 61 patients were enrolled in the study: 35 renal transplant recipients and 26 patients with NDD-CKD. The two groups were well matched in age, sex, and ethnicity. The patients represented a heterogeneous sample of CKD, and disease etiology represented an assortment of causes. Baseline mean estimated glomerular filtration rate was 37.6 mL/min/1.73 m2 in the NDD-CKD patients and 53.6 mL/min/1.73 m2 in the renal transplant patients.
Overall, BIA was strongly comparable to DXA estimated body composition. In the renal transplant recipient group, compared with DXA, BIA overestimated LM by 2.1 kg, although intraclass correlation coefficient (ICC) showed “excellent” agreement along with an r2 value of 0.99. BIA underestimated fat mass (FM) (–2.1) and body fat % (BF%) (–3.8), although both showed “excellent” (ICC r=.972 and .954) agreement, respectively. In the NDD-CKD patient group, BIA tended to overestimate LM and underestimate both FM and BF%. All showed “excellent” (ICC r=.980, .967, and .927) agreement respectively.
The Hume formula overestimated LM in both patient groups (3.5 in the renal transplant group and 3.6 in the NDD-CKD group); however, both showed “excellent” agreement (ICC r=.960 and .950, respectively). The Hume formula was able to estimate FM with “remarkable” accuracy compared with DXA. For patients in the renal transplant recipient group, Hume formula-derived FM was 0.3 kg difference (ICC r=.960, “excellent”), and in the NDD-CKD patient group, only 0.1 kg difference (ICC r=.947 “excellent”). For both groups, the Hume formula underestimated BF% (ICC r showed “good” correlation for both [r=.859 for renal transplant recipients and r=.808 for NDD-CKD patients]).
The study was limited by the relatively small sample size.
In summary, the researchers said, “The Hume formula may reliably predict the same parameters obtained by DXA in both renal transplant recipients and NDD-CKD patients. Notably, the Hume formula does not require any additional equipment and uses routinely collected parameters including height and BM. With the addition of age and sex, this formula provides a superior wealth of body composition information over the routinely used, but largely inadequate, BMI. In addition, body composition estimated by BIA also provided similar estimates versus DXA. Thus, both the Hume formula and BIA could provide simple and inexpensive means to estimate body composition in renal disease.”
- Researchers in the United Kingdom conducted a cohort study to determine the validity of the Hume equation and bioelectrical impedance analysis (BIA) as an estimate of body composition compared with dual-energy x-ray absorptiometry (DXA).
- The study cohort included 35 renal transplant recipients and 29 patients with nondialysis-dependent chronic kidney disease.
- Both the Hume formula and BIA provided a superior composite of data on body composition, compared with DXA, in both groups.