Canaud B, Leblanc M, Garred L J, Bosc J Y, Argilés A, Mion C
Department of Nephrology, Lapeyronie University Hospital, Montpellier, France.
Am J Kidney Dis. 1997 Nov;30(5):672-9. doi: 10.1016/s0272-6386(97)90492-3.
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 generation rate using urea kinetic modeling (UKM), but the normalizing factor is still a matter of controversy. By convention, PCR is expressed in 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 and that body composition is preserved with a lean body mass (LBM) over BW ratio near 0.73. Such conditions being infrequently found in dialysis patients, it has been proposed to normalize PCR to ideal BW or to total body water, but these correction factors are not really appropriate. A more rational approach would be to express PCR 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 nitrogen reserve. In this study, we developed a combined kinetic model of urea and creatinine applied to the midweek dialysis cycle in 66 end-stage renal disease (ESRD) patients. UKM provided Kt/V and PCR, whereas creatinine kinetic modeling (CKM) was used to calculate LBM. Thirty-four 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 normalized to BW (nPCRBW) and of 1.40 +/- 0.30 g/kg/24 h when normalized to LBM (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, with 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 abnormal body composition (eg, obese patients) and permits PCR to be adjusted for the decrease in LBM that occurs with age. We propose nPCRLBM as a more rational index to express PCR in dialysis patients.
蛋白质分解代谢率（PCR），等同于“稳定”透析患者的膳食蛋白质摄入量，被广泛认为是其蛋白质营养状况的一个指标。PCR通常通过尿素动力学建模（UKM）从尿素生成率来确定，但归一化因子仍是一个有争议的问题。按照惯例，PCR以每日降解的蛋白质克数除以干体重（BW）来表示（nPCRBW）。要使该指标有效，这意味着干体重接近理想体重，并且身体组成得以保持，瘦体重（LBM）与体重的比值接近0.73。而透析患者很少具备这些条件，因此有人提议将PCR归一化到理想体重或总体水，但这些校正因子并不十分合适。一种更合理的方法是将PCR表示为蛋白质降解量与LBM千克数的比值（nPCRLBM），这样做的主要优点是能直接将PCR与蛋白质或氮储备的变化联系起来。在本研究中，我们开发了一种尿素和肌酐的联合动力学模型，并将其应用于66例终末期肾病（ESRD）患者的周中透析周期。UKM提供了Kt/V和PCR，而肌酐动力学建模（CKM）用于计算LBM。34例LBM保持正常（LBM/干体重比值等于或大于0.70；平均比值为0.81±0.11）且干体重/理想体重比值为1.01±0.16的患者，当以体重归一化时（nPCRBW），平均PCR为1.14±0.30克/千克/24小时，以LBM归一化时（nPCRLBM）为1.40±0.30克/千克/24小时。在32例LBM降低（LBM/干体重比值低于0.70；平均比值为0.60±0.09）且干体重/理想体重比值为1.11±0.23的患者中，平均nPCRBW为0.99±0.31克/千克/24小时，而nPCRLBM为1.62±0.32克/千克/24小时。对于这两个亚组，Kt/V相似，平均值分别为1.76±0.34和1.69±0.27。将PCR归一化到LBM有双重益处：它补偿了由异常身体组成（如肥胖患者）引起的误差，并允许根据年龄增长导致的LBM下降对PCR进行调整。我们提议将nPCRLBM作为透析患者中表达PCR的更合理指标。
