ESTIMATION OF TOTAL DAILY CREATININE CLEARANCE IN CAPD FROM SERUM CREATININE CONCENTRATION

Objective: To establish whether estimation of creatinine clearance (Cr Cl) from serum creatinine, gender, age, and weight might reduce the nu mber of 24-hour urine and dialysate collections required to monitor ad equacy of delivered dialysis on continuous ambulatory peritoneal dialy sis (CAPD). Design: Retrospective single-center study. Setting: Univer sity Hospital. Patients: Creatinine excretion and CrCl were measured i n 187 24-hour urine and dialysate collections from 99 CAPD patients (5 5 male, 44 female). Multiple regression analysis was used to estimate creatinine excretion from age and weight in males and females. CrCl wa s derived and also calculated using the Cockcroft-Gaultand Mitch-Walse r formulas. Positive and negative predictive values for indicating ade quacy of dialysis were determined. Results: Measured and derived CrCl were correlated (males: r = 0.85; females: r = 0.83; p < 0.001), but a greement was poor (95% limits of agreement: males, 26.05 to -25.75 L/w k; females, 37.47 to -19.49 L/wk). Taking the minimum acceptable CrCl as 60 L/week, the respective positive predictive values of the derived , Cockcroft, and Mitch methods in predicting underdialysis were 88%, 1 00%, and 100% in males and 88%, 88%, and 89% in females. Negative pred ictive values were 83%, 57%, and 53% in males and 53%, 48%, and 45% in females. Conclusion: A derived CrCl > 60 was not predictive of adequa te dialysis. Because the detection of underdialysis is our objective, formal clearance studies should be performed in this group. A derived CrCl < 60 L/wk was predictive of underdialysis in males and females an d an increase in dialysis dose without formal clearance measurements c ould be suggested in these patients. The use of this approach could al low an important reduction in the number of clearance studies required to monitor CAPD adequacy.