Estimating glomerular filtration rate: Cockcroft-Gault and Modification of Diet in Renal Disease formulas compared to renal inulin clearance

Abstract

Background and objectives: Evaluation of renal function by estimation of the glomerular filtration rate (GFR) is very important for the diagnosis and treatment of patients with chronic kidney disease (CKD). The Cockcroft-Gault (CG) and Modification of Diet in Renal Disease (MDRD) formulas are the most commonly used estimations.

Design, setting, participants, & measurements: Estimated GFR values by each formula were compared with measured GFR (mGFR) by renal inulin clearance in 2208 European adults (46% women, 1.4% Caribbean blacks), with and without CKD, and mean mGFR 72.4 +/- 39.0 (range 2.2 to 177.2) ml/min/1.73 m(2).

Results: Overall, the CG and MDRD formulas showed bias (mean difference) -3.5 ml/min/1.73 m(2) (5.3%), P < 0.001, and -9.8 ml/min/1.73 m(2) (-6.4%), P < 0.001; precision (SD of bias) 21.5 ml/min/1.73 m(2) (43.1%) and 20.0 ml/min/1.73 m(2) (33.0%); limits of agreement (2 SD by Bland-Altman method) 39.5 to -46.5 (range 86.0) ml/min/1.73 m(2) and 30.2 to -49.8 (range 80.0) ml/min/1.73 m(2); and accuracy within +/-30% of mGFR 70.8 and 69.0%, respectively. Both formulas showed a trend for decreasing accuracy with lower mGFR levels. According to the Kidney Disease Outcomes Quality Initiative (K/DOQI)-CKD classification's five GFR groups, the CG and MDRD formulas properly assigned 61.6 and 57.1% of the entire population and had a range of positive predictive values 42.6 to 81.8% and 39.6 to 85.2% and of negative predictive values 81.7 to 96.6% and 76.4 to 97.5%, respectively.

Conclusions: The CG and MDRD formulas had some limitations for proper GFR estimation and K/DOQI-CKD classification by GFR levels alone.

Figure 1.

Relation between serum creatinine concentration and measured glomerular filtration rate (GFR) by renal inulin clearance.

Figure 2.

Relation of measured glomerular filtration rate (GFR) by renal inulin clearance and estimated GFR (eGFR) by (A) Cockcroft-Gault (CG) formula and (B) Modification of Diet in Renal Disease (MDRD) formula. Trend line in bold; r², variability coefficient.

Figure 3.

Bland and Altman plots comparing measured glomerular filtration rate (GFR) by renal inulin clearance and estimated GFR (eGFR) by (A) Cockcroft-Gault (CG) formula and (B) Modification of Diet in Renal Disease (MDRD) formula. Bold lines define upper (+2 SD) and lower (−2 SD) limits of agreement; dashed lines represent mean difference between eGFR and inulin GFR.