PROTEIN CATABOLIC RATE OVER LEAN BODY-MASS RATIO - A MORE RATIONAL APPROACH TO NORMALIZE THE PROTEIN CATABOLIC RATE IN DIALYSIS PATIENTS

Protein catabolic rate (PCR), equivalent to dietary protein intake in ''stable'' dialysis patients, is widely accepted as a marker of their protein nutritional status. PCR is usually established from urea gener ation rate using urea kinetic modeling (UKM), but the normalizing fact or is still a matter of controversy. By convention, POR is expressed i n grams of protein degraded daily divided by the dry body weight (BW) (nPCRBW). To be valid, this implies that dry BW is close to ideal BW a nd that body composition is preserved with a lean body mass (LBM) over BW ratio near 0.73. Such conditions being infrequently found in dialy sis patients, it has been proposed to normalize PCR to ideal BW or to total body water, but these correction factors are not really appropri ate. A more rational approach would be to express POR as the ratio of protein degraded to the kilograms of LBM (nPCRLBM), thus offering the main advantage of directly coupling PCR to changes in protein or nitro gen reserve. In this study, we developed a combined kinetic model of u rea and creatinine applied to the midweek dialysis cycle in 66 end-sta ge renal disease (ESRD) patients. UKM provided Kt/V and PCR, whereas c reatinine kinetic modeling (CKM) was used to calculate LBM. Thirty-fou r patients with a preserved LBM (LBM/dry BW ratio equal to or greater than 0.70; mean ratio, 0.81 +/- 0.11) and with a dry/ideal BW ratio of 1.01 +/- 0.16 had a mean PCR of 1.14 +/- 0.30 g/kg/24 h when normaliz ed to BW (nPCRBW) and of 1.40 +/- 0.30 g/kg/24 h when normalized to LB M (nPCRLBM). In the 32 patients with a reduced LBM (LBM/dry BW ratio, below 0.70; mean ratio, 0.60 +/- 0.09) and dry/ideal BW ratio of 1.11 +/- 0.23, the mean nPCRBW was 0.99 +/- 0.31 g/kg/24 h, whereas nPCRLBM was 1.62 +/- 0.32 g/kg/24 h. For both subgroups, Kt/V was similar, wi th mean values of 1.76 +/- 0.34 and 1.69 +/- 0.27. Normalizing PCR to LBM offers a double benefit: it compensates for the error induced by a bnormal body composition (eg, obese patients) and permits PCR to be ad justed for the decrease in LBM that occurs with age. We propose nPCRLB M as a more rational index to express PCR in dialysis patients. (C) 19 97 by the National Kidney Foundation, Inc.