Estimating Dietary Protein and Sodium Intake with Sodium Removal in Peritoneal Dialysis Patients

An increase in dietary protein intake (DPI) carries a risk with respect to increased sodium intake, which further leads to the development of cardiovascular morbidity in peritoneal dialysis (PD) patients. Dialytic (DSR) and urinary sodium removal (USR) are potential indicators of sodium intake. In this single-center cross-sectional study with 60 prevalent PD patients, we analyze the correlation of DPI with sodium intake and the association between residual renal function (RRF) and comorbidity grade, expressed as the Davies score with sodium removal and protein metabolism indices such as normalized protein catabolic rate (nPCR) and lean body mass (LBM). The value of RRF < 2 mL/min/1.73 m² is significantly associated with lower USR (p = 0.000) and lower %LBM (p < 0.001). The greatest USR is detected in patients with low Davies comorbidity grade (p = 0.018). Compared to patients with DPI < 0.8 g/kg/day, patients with DPI > 0.8 g/kg/day have a greater sodium intake (3.69 ± 0.71 vs. 2.94 ± 0.86; p < 0.018) and a greater nPCR (p < 0.001). Protein intake is significantly correlated with sodium intake (p = 0.041), but not with total sodium removal (TSR). A strong correlation is observed between sodium intake and TSR (p = 0.000), although single TSR values are not the same as the corresponding sodium intake values. An increasing protein intake implies the necessity to determine both sodium intake and sodium removal. Preservation of RRF has a beneficial role not just in sodium removal, but also in the increase of LBM.