Normalization of protein nitrogen appearance by various size indicators in patients on continuous peritoneal dialysis

Protein nitrogen appearance (PNA) estimated from urea nitrogen appearance (UNA) reflects dietary protein intake and is an important index of nutrition in peritoneal dialysis (PD). Normalization of PNA by several body size indicators has resulted in discrepancies between normalized PNA (nPNA) values and other nutrition indices in PD patients with varying weight status. To test whether a particular size indicator produces nPNA values that eliminate the discrepancies, we normalized PNA values obtained at the first clearance study in 925 PD patients by weight (W), by fat-free mass (FFM) obtained from body water, by lean body mass (LBM) derived from creatinine kinetics, by desirable weight (DW), by standard weight (SW), and by adjusted edema-fee body weight (aBW). We classified patients into three groups according to W/DW: an underweight group [group I: W/DW < 0.9, n = 147 (15.9%)], a normal-weight group [group II: 0.9 < or = W/DW < 1.2, n = 506 (54.7%)], and an obese group [group III: W/DW > or = 1.2, n = 272 (29.4%)]. The UNA and PNA increased progressively from group I to group III. The W, FFM, LBM, SW, and aBW also increased progressively, and the corresponding nPNA values decreased progressively from group I to group III--all at p < 0.001. The DW did not differ significantly between the three groups. The PNA values normalized by DW were 0.91 +/- 0.21 (group I), 0.96 +/- 0.24 (group II), and 1.07 +/- 0.25 (group III), p < 0.001. Of the six size indicators tested, only DW produced values of nPNA consistent with the nutrition status of PD patients with varying weight status. Our findings indicate that DW is the proper size indicator for normalizing PNA in PD patients.