The Relationship between Kt/V Urea and Npna in Anuric Peritoneal Dialysis Patients: A Comparison with Predialysis Patients

OBJECTIVE: It is unknown whether a given level of urea clearance by the native kidneys provides better or similar control of uremia than the same level of urea clearance by continuous peritoneal dialysis (PD). More insight into possible differences between renal and peritoneal urea clearances is warranted. Therefore, we investigated the relationship between Kt/V(urea) and protein equivalent of total nitrogen appearance normalized to body weight (nPNA), the relationship between urea clearance and creatinine appearance, and other nutritional parameters in PD patients without residual renal function, and in predialysis end-stage renal disease patients. PATIENTS: All patients participated in the Netherlands Cooperative Study on the Adequacy of Dialysis. This is a prospective cohort study of incident dialysis patients, in whom regular assessments of renal function are done. A group of 75 PD patients was identified at the first follow-up assessment in which their urine production was less than 100 mL/day. These patients were considered the anuric group. This group was compared with a control group of 97 predialysis patients studied 0-4 weeks before the start of dialysis treatment. RESULTS: Linear relationships were present between Kt/V(urea) and nPNA, in both the predialysis patients and the anuric PD patients. A significant difference was present between the slopes of the two regression lines (0.40 vs 0.18, p = 0.007). When Kt/V(urea) exceeded 1.3/week, a given level of Kt/V(urea) was associated with a higher nPNA in predialysis than in anuric PD patients. Similar relationships were found between Kt(urea) and PNA. Kt(urea) was also significantly related to urine or dialysate creatinine appearance. A significant difference existed between the slopes of the regression lines in the two groups of patients (p < 0.001). A weekly Kt(urea) of 70 L was associated with a urine creatinine appearance of 11.0 mmol/day and a dialysate creatinine appearance of 8.4 mmol/day. Nutritional status measured with creatinine appearance and Subjective Global Assessment was better in the predialysis population, despite much lower values for Kt/V(urea) in these patients. CONCLUSIONS: The relationship between Kt/V(urea) and nPNA in anuric PD patients is different from that in a predialysis population. It follows from our results that, when Kt/V(urea) is above 1.3/week, a given level of Kt/V(urea) is associated with a higher nPNA in predialysis than in anuric PD patients. This challenges the concept of equivalency between renal and peritoneal Kt/V(urea) with respect to control of uremic morbidity.