Validation of the Modification of Diet in Renal Disease formula for estimating GFR with special emphasis on calibration of the serum creatinine assay.
BACKGROUND
The Modification of Diet in Renal Disease (MDRD) formula is recommended by European and American guidelines for estimating glomerular filtration rate (GFR). However, the accuracy of the formula has been questioned in several studies. Our objective is to evaluate the performance of the MDRD formula with special emphasis on the possibility that interlaboratory calibration differences for serum creatinine reduce the accuracy of the formula.


METHODS
The MDRD and 7 other commonly used formulae were evaluated regarding bias, precision, and accuracy. The 215 adults included were patients with chronic kidney disease, potential kidney donors, and patients referred before nephrotoxic chemotherapy. Serum creatinine was measured by means of a kinetic Jaffé method (Hitachi 917, Hitachi, Tokyo, Japan; reagents from Roche Diagnostics, Mannheim, Germany). GFR, measured as plasma clearance of chromium 51-labeled EDTA (Cr-EDTA), ranged from 3 to 162 mL/min/1.73 m2.


RESULTS
The MDRD formula was heavily biased, but it still had significantly better accuracy than the other formulae tested. After recalibrating our serum creatinine values (serum creatinine [mg/dL] = -0.215 + 1.08 * serum creatinine), systematic bias was greatly reduced and better accuracy was achieved: 45.6% of results differed less than 15% from Cr-EDTA, 64.2% differed less than 30%, and 81.4% differed less than 50%. The equation for recalibrating creatinine values was based on data with traceability to reference methods and on sensitivity analysis.


CONCLUSIONS
The MDRD formula seems to be the best formula available for GFR estimating, but it is based on a serum creatinine method calibrated to give much lower values than most laboratories, leading to underestimation of GFR in mild renal insufficiency.
Hallan
Stein
S
Department of Medicine, Division of Nephrology, St Olavs Hospital/NTNU, Trondheim, Norway. stein.hallan@medisin.ntnu.no
Asberg
Arne
A
Lindberg
Morten
M
Johnsen
Harald
H
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002138:Calibration; D002908:Chronic Disease; D003404:Creatinine / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007674:Kidney Diseases / Q000175:diagnosis*; D007677:Kidney Function Tests / Q000592:standards*; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000592:standards; D012189:Retrospective Studies; D012680:Sensitivity and Specificity
D003404:Creatinine