Influence of changes in peritoneal fluid on body-composition measurements by dual-energy X-ray absorptiometry in patients receiving continuous ambulatory peritoneal dialysis

The effect of the presence of intraabdominal fluid on measurement of body composition by dual-energy X-ray absorptiometry (DXA) was determined by scanning 14 patients who were receiving continuous ambulatory peritoneal dialysis (CAPD) before and after the drainage of peritoneal dialysate, resulting in a mean (+/- SD) weight loss of 1.81 +/- 0.34 kg. DXA showed changes in whole-body soft tissue, which were correctly localized to the trunk region on regional analysis. Changes in DXA estimates of mean total lean tissue, 1.78 +/- 0.94 kg, and trunk lean tissue, 1.87 +/- 0.84 kg, were very similar to the actual change in body weight. However, the DXA estimate of change in total soft tissue, 2.11 +/- 0.44 kg, was significantly greater than the change in body weight by 0.3 kg (P < 0.005); the difference was accounted for by a tendency for a reduction in the estimate of body fat affecting the trunk region after drainage of dialysate. DXA was also less good at detecting changes in individual subjects. Estimates of total and regional bone mineral content and bone mineral density were not affected by the drainage of the dialysis fluid.