Novel equations to estimate lean body mass in maintenance hemodialysis patients

Abstract

Background: Lean body mass (LBM) is an important nutritional measure representing muscle mass and somatic protein in hemodialysis patients, for whom we developed and tested equations to estimate LBM.

Study design: A study of diagnostic test accuracy.

Setting & participants: The development cohort included 118 hemodialysis patients with LBM measured using dual-energy x-ray absorptiometry (DEXA) and near-infrared (NIR) interactance. The validation cohort included 612 additional hemodialysis patients with LBM measured using a portable NIR interactance technique during hemodialysis.

Index tests: 3-month averaged serum concentrations of creatinine, albumin, and prealbumin; normalized protein nitrogen appearance; midarm muscle circumference (MAMC); handgrip strength; and subjective global assessment of nutrition.

Reference test: LBM measured using DEXA in the development cohort and NIR interactance in validation cohorts.

Results: In the development cohort, DEXA and NIR interactance correlated strongly (r = 0.94, P < 0.001). DEXA-measured LBM correlated with serum creatinine level, MAMC, and handgrip strength, but not with other nutritional markers. Three regression equations to estimate DEXA-measured LBM were developed based on each of these 3 surrogates and sex, height, weight, and age (and urea reduction ratio for the serum creatinine regression). In the validation cohort, the validity of the equations was tested against the NIR interactance-measured LBM. The equation estimates correlated well with NIR interactance-measured LBM (R² ≥ 0.88), although in higher LBM ranges, they tended to underestimate it. Median (95% confidence interval) differences and interquartile range for differences between equation estimates and NIR interactance-measured LBM were 3.4 (-3.2 to 12.0) and 3.0 (1.1-5.1) kg for serum creatinine and 4.0 (-2.6 to 13.6) and 3.7 (1.3-6.0) kg for MAMC, respectively.

Limitations: DEXA measurements were obtained on a nondialysis day, whereas NIR interactance was performed during hemodialysis treatment, with the likelihood of confounding by volume status variations.

Conclusions: Compared with reference measures of LBM, equations using serum creatinine level, MAMC, or handgrip strength and demographic variables can estimate LBM accurately in long-term hemodialysis patients.

Figure 1

Flow diagram of the development and the validation cohort LBM, lean body mass; DEXA, Dual energy X-ray absorptiometry; SCr; serum creatinine; MAMC, mid arm muscle circumference; HGS, handgrip strength, NIR: near infra-red

Figure 2

Box plots of LBM measured directly be DEXA and estimated indirectly by SCr, MAMC, and handgrip strength using different 3 regression equations (see text) in the development cohort of 118 hemodialysis patients. The lower and upper box boundaries are the 25^th and 75^th percentiles, the line within the box is the median, and the whiskers extend to min and max. LBM, lean body mass; DEXA, Dual energy X-ray absorptiometry; SCr; serum creatinine; MAMC, mid arm muscle circumference; HGS, handgrip strength

Figure 3

Difference plots between LBM using NIR interactance as reference standard and the 2 equations based on SCr and MAMC in the validation cohort of 612 hemodialysis patients. Medium dashed line is the difference, long dashed lines are limits of agreement (mean±2SD) and short dashed lines are 95% confidence intervals for the difference. LBM, lean body mass; DEXA, Dual energy X-ray absorptiometry; NIR, near-infrared; SCr; serum creatinine; MAMC, mid arm muscle circumference.

Figure 4

Scatter plots, regression line and 95% confidence intervals, reflecting the correlations between the NIR interactance-measured LBM and the LBM estimated by MAMC (Panel A) and SCr (Panel B) in the validation cohort of 612 hemodialysis patients. Shaded areas reflect the 95% confidence intervals. LBM, lean body mass; NIR, near-infrared; SCr; serum creatinine; MAMC, mid arm muscle circumference.