Body composition following hemodialysis: studies using dual-energy X-ray absorptiometry and bioelectrical impedance analysis

The detection, prevention and treatment of disease is greatly facilitated by the availability of accurate and non-invasive techniques for measuring the amount and regional distribution of fat mass and fat-free mass. As differing degrees of hydration may influence these measurements, we used dual-energy X-ray absorptiometry (DXA) and bioelectrical impedance analysis (BIA) to detect changes in hydration following hemodialysis, and to determine whether fat mass, fat-free mass and bone density measurements were affected by these fluid changes. Ten subjects (7 men, 3 women) mean age 46.2 years (range 25-68 years), with renal failure had bone density, fat-free mass and fat mass measured by DXA, and total body water and fat-free mass measured by BIA, before and after hemodialysis. Thirty-two subjects had fat-free mass measured by DXA and BIA in an attempt to derive new equations (using fat-free mass measured by DXA as the reference standard) to improve the predictive value of BIA. The new equations were then used to derive the changes in fat-free mass following hemodialysis measured using BIA. In absolute terms, total tissue measured by DXA (r = 0.99, p = 0.01) and total body water measured by BIA (r = 0.91, p = 0.01) correlated with gravimetric weight. Following hemodialysis, fat mass and bone density measured by DXA were unaffected by the fluid changes. The change in gravimetric weight was 1.8 +/- 0.3 kg, p = 0.01 (mean +/- SEM). This change was measured as 1.9 +/- 0.3 kg by DXA, -0.9 +/- 1.0 kg by BIA using the published equation for fat-free mass, and 3.2 +/- 0.4 kg using the new equation for fat-free mass.