Currently, weekly KT/V and weekly creatinine clearance (WCC) are used to quantitate continuous ambulatory peritoneal dialysis (CAPD), the minimum recommended requirements being 1.7/week and 50 L/week, respectively. There is no substantial evidence that one index is better than the other, and there is no clear recommendation what one should do if there is a discrepancy between these two values. We performed a cross sectional analysis of 68 patients in whom we measured weekly KT/V, WCC, residual clearances, and a 4-hr peritoneal equilibration test (PET). The correlation between KT/V and WCC in the whole group was highly significant (p < 0.0001); when patients were divided in the four PET groups, there was a significant correlation (p < 0.05) in the low-average (n = 22) and high-average (n = 21) PET groups, but the correlation was not significant in the high (n = 13) and low (n = 12) PET groups. Fourteen of 68 patients (20%) showed a discrepancy between KT/V and WCC: 7 patients had a KT/V < 1.7 and WCC > or = 50 (group 1), and 7 patients had a KT/V > or = 1.7 and WCC < 50 (group 2). Those in group 1 with a WCC > 50 had a higher residual renal function (0.82 vs 0.11 mL/min, p < 0.05) than those in group 2 and therefore had a higher tubular secretion of creatinine and reabsorption of urea. Those in group 2 with a KT/V > 1.7 had lower creatinine equilibration than those in group 1 (D/Pcr 0.56 vs 0.75, p < 0.05) and therefore a better removal of urea than creatinine.(ABSTRACT TRUNCATED AT 250 WORDS)