4-COMPONENT MODEL OF BODY-COMPOSITION IN CHRONIC-RENAL-FAILURE COMPRISING DUAL-ENERGY X-RAY ABSORPTIOMETRY AND MEASUREMENT OF TOTAL-BODY WATER BY DEUTERIUM-OXIDE DILUTION

1. Assessment of nutrition in patients with chronic renal failure by b ody composition measurement techniques may be affected by variable hyd ration, 2. This study aimed to derive a four-component model of body c omposition (consisting of fat, protein, total body water and body mine ral) from a combination of dual-energy X-ray absorptiometry and total body water measured by deuterium oxide dilution, allowing assessment o f body protein stores without the effect of variation in hydration, Pa tients with chronic renal failure on haemodialysis, peritoneal dialysi s and conservative treatment and a control group were studied, Patient s with chronic renal failure were at an 'ideal' state of hydration on clinical assessment. 3. Hydration was defined by total body water as a percentage of fat-free mass measured by dual-energy X-ray absorptiome try, and no differences were found between chronic renal failure subgr oups and control subjects (except in the female undialysed chronic ren al failure subgroup), Hydration was significantly correlated with perc entage total body fat in the control groups but not in patients with c hronic renal failure. 4. Lean tissue measured by dual-energy X-ray abs orptiometry was significantly reduced in three of the six chronic rena l failure groups compared with control subjects (male and female patie nts on haemodialysis and female patients on peritoneal dialysis), Prot ein estimated from the four-component model failed to detect these abn ormalities, 5. Lean tissue measured by dual-energy X-ray absorptiometr y in normal subjects strongly correlated with fat-free mass measured b y total body potassium in normal subjects (male r = 0.91; female r = 0 .89, both P < 0.0001), The correlation of protein estimated from the f our-component model with fat-free mass measured by total body potassiu m was far weaker in male control subjects (r = 0.51, P<0.05) and not s ignificant in female control subjects (r = 0.38, P not significant), I n the normal subjects protein estimated from the four-component model showed a much greater variation from protein estimated by total body p otassium than did protein estimated simply as 27% of dual-energy X-ray absorptiometry fat-free mass minus total body mineral. 6. Hydration i n patients with chronic renal failure in whom fluid balance is believe d to be normal on clinical criteria does not differ from that in norma l subjects, The combined model of dual-energy X-ray absorptiometry and total body water is not a useful method for the measurement of body p rotein.