Estimation of glomerular filtration rate in older patients with chronic renal insufficiency: is the modification of diet in renal disease formula an improvement?

OBJECTIVES

To evaluate a new formula for glomerular filtration rate (GFR), derived from the Modification of Diet in Renal Disease (MDRD) study in older people.

DESIGN

An observational study of the performance of the MDRD formula compared with other formulae and creatinine clearance (ClCr) as measures of the GFR.

SETTING

Volunteers were recruited via outpatient clinics.

PARTICIPANTS

Fifty-two patients (27 men, 25 women: mean age 80, range 69-92) with a variety of medical diagnoses. Mean GFR was 53.3 mL/min/1.73 m2 (range 15.9-100.2). Exclusion criteria included renal replacement therapy/renal transplantation and cognitive impairment.

MEASUREMENTS

51Chromium ethylenediaminetetraacetic acid (51Cr EDTA) was used as the reference method against which the formulaic estimates of GFR were compared using bias plot and regression analyses.

RESULTS

The MDRD and Cockcroft and Gault formulae (both coefficient of determination (R2) = 0.84) gave the best fit with GFR, followed by the Jelliffe formula (R2 = 0.81), ClCr (R2 = 0.73) and the Baracskay formula (R2 = 0.56). ClCr (-1.2%) demonstrated minimal bias compared with the MDRD (8.0%) and Cockcroft and Gault (-10.4%) formulae. However, imprecision compared with 51Cr EDTA was lowest for the Cockcroft and Gault formula, with 50% of estimates lying between -9.5 and -0.5 mL/min/1.73 m2 of measured 51Cr EDTA clearance. This compares with -6.7 and 10.1 mL/min/1.73 m2 for ClCr and 0.0 and 12.7 mL/min/1.73 m2 for the MDRD formula.

CONCLUSION

Calculated estimates of GFR are an improvement over ClCr estimation. On balance, the MDRD formula does not improve the estimate of GFR compared with the Cockcroft and Gault formula in older Caucasian patients with chronic renal insufficiency.