Effects of fluid retention on the measurement of body composition using bioelectric impedance.

Body composition measurements using bioelectrical impedance analysis (BIA) were performed on 50 uremic patients immediately before and after hemodialysis (HD) therapy, on 10 uremic patients under continuous ambulatory peritoneal dialysis (CAPD) therapy before and after the fluid was drained out of the peritoneal cavity and on 3 cirrhotic patients before and after abdominal paracentesis. Thirty-two pairs of measurements were performed on the CAPD patients and 3 pairs on the cirrhotic patients. Significant increases in both resistance and reactance were noted after HD. However, resistance and reactance before and after peritoneal fluid had been drained were not significantly different. In HD, body fluid loss as estimated by BIA (LBIA) was higher than that from the body weight method (LBW). The relationship between the two is described by the equation LBW = 0.841LBIA + 0.588. The total body fat estimated before HD was significantly lower than after HD, and it was significantly higher when measured with peritoneal fluid retention than with fluid drained. Generalized edema caused an increase in resistance and reactance, while local peritoneal fluid retention did not cause any significant changes. When total body fluid is measured by the BIA method, it is often overestimated in the case of generalized edema and underestimated in case of peritoneal fluid retention. Therefore, total body fat is underestimated by BIA in generalized edema before HD and overestimated in peritoneal fluid retention.