Background: Indirect methods such as anthropometry (A), Watson formula (W), creatinine kinetics (CK), and body electrical impedance (BEI) are increasingly applied to determine total body water (TBW) and lean body mass (LBM) in dialysis patients. These methods share the disadvantage that they have been validated for healthy men only. We studied which of these four commonly applied methods can best be used routinely in CAPD patients.
Methods: TBW estimates obtained from A, W, CK, and BEI were compared with those obtained by a gold standard (antypirine distribution volume, ADV) in eight CAPD patients. In addition, several BEI equations to derive lean body mass (LBM) were compared with LBM estimated by ADV in order to determine which equation is the most valuable for the assessment of LBM by BEI in CAPD patients.
Results: TBW as ADV was 41.4 +/- 6.6 (mean +/- SD) L. TBW estimated by W, A and CK underestimated ADV by a mean +/- SD of 2.3 +/- 13, 5 +/- 8.4 and 12.3 +/- 10.9% respectively. TBW as measured by BEI overestimated ADV by 2.5 +/- 8.8%. The correlation coefficients between ADV-TBW and TBW estimated by the indirect methods were r = 0.88 (A), r = 0.87 (BEI), r = 0.82 (CK), and 0.68 (W). LBM estimated by ADV was 56.7 +/- 8.9 (mean +/- SD) kg; LBM by different BEI equations ranged from 49.9 +/- 7 to 58.1 +/- 10.7 kg. The correlation coefficient between LBM by ADV and LBM according to the various BEI equations ranged from 0.81 to 0.93.
Conclusion: A and BEI can be used to estimate TBW, but the considerable SD (or inaccuracy) makes individual predictions hazardous. Considering the correlation coefficients and difference between LBM by ADV and LBM according to different BEI equations, Deurenberg's formula can be advocated for use in the estimation of LBM by BEI.