Glomerular filtration rate (GFR) estimated from serum creatinine predicts total (urine and peritoneal) creatinine clearance in patients on peritoneal dialysis.

Objectives: The aim of this study was to examine the accuracy of the Modification of Diet in Renal Disease (MDRD) equation and the Cockcroft and Gault formula (CCrCG) in predicting total creatinine clearance achieved by residual renal function plus peritoneal dialysis in patients on chronic peritoneal dialysis.

Methods: Total creatinine clearance was defined as peritoneal creatinine clearance (PCcr) plus the average of urine urea and creatinine clearances (cGFR). Correlation analysis and Bland-Altman plot were used to establish the degree of correlation and agreement between the estimations of creatinine clearance achieved by PCcr and the average of cGFR and estimated creatinine clearance based on serum creatinine by using either MDRD equation or the Cockcroft and Gault formula.

Results: In one hundred fifty-six measurements, mean clearances by [cGFR + PCcr], CCrCG and MDRD were: 7.9 ± 3.1, 10.6 ± 5.2 and 8.5 ± 4.9 ml/min/1.73 m(2), respectively. There was a good correlation between [cGFR + PCcr] and MDRD (r = 0.776, P < 0.05) and [cGFR + PCcr] and CCrCG (r = 0.735, P < 0.05). The mean MDRD was not significantly different from the mean clearance by [cGFR + PCcr] (difference 0.4 ± 2.9 ml/min/1.73 m(2), agreement limit -5.4-6.3 ml/min/1.73 m(2)). The CCrCG formula gave a larger difference from the mean [cGFR + PCcr] (2.8 ± 10.5 ml/min/1.73 m(2)) and a much wider agreement limit (-3.7-9.3 ml/min/1.73 m(2)). In male patients, MDRD formula provided an estimate of clearance that was similar to the mean [cGFR + PCcr] (7.9 ± 3.8 ml/min/1.73 m(2) vs. 8.2 ± 3.2 ml/min/1.73 m(2), respectively; difference 0.10 ± 1.9 ml/min/1.73 m(2), limits of agreement -3.9-3.7 ml/min/1.73 m(2)). By contrast, in female patients, the MDRD equation significantly overestimated the clearance (difference between mean estimated and mean measured clearance 1.4 ± 4.1 ml/min/1.73 m(2), limits of agreement -6.6-9.5 ml/min/1.73 m(2) P < 0.05). In conclusion, the GFR estimated by MDRD formula is similar to [cGFR + PCcr] especially in males. GFR by the CCrCG formula tended to overestimate the highest values of [cGFR + PCcr].