Expressing the Modification of Diet in Renal Disease Study equation for estimating glomerular filtration rate with standardized serum creatinine values.
OBJECTIVE
We sought to reexpress the 4-variable Modification of Diet in Renal Disease (MDRD) Study equation for estimation of glomerular filtration rate (GFR) using serum creatinine (S(cr)) standardized to reference methods.


METHODS
Serum specimens included creatinine reference materials prepared by the College of American Pathologists (CAP), traceable to primary reference material at the NIST, with assigned values traceable to isotope dilution mass spectrometry (IDMS), a calibration panel prepared by the Cleveland Clinic Research Laboratory (CCRL), and frozen samples from the MDRD Study. Split specimens were measured at the CCRL using the Roche enzymatic and Beckman CX3 kinetic alkaline picrate assays.


RESULTS
Roche enzymatic assay results on CAP samples were comparable to IDMS-assigned values. Beckman CX3 assay results in 2004-2005 were significantly higher than but highly correlated with simultaneous Roche enzymatic assay results (r(2) = 0.9994 on 40 CCRL samples) and showed minimal but significant upward drift from Beckman CX3 assay results during the MDRD Study in 1989-1991 (r(2) = 0.9987 in 253 samples). Combining these factors, standardized S(cr) = 0.95 x original MDRD Study S(cr). The reexpressed 4-variable MDRD Study equation for S(cr) (mg/dL) is GFR = 175 x standardized S(cr)(-1.154) x age(-0.203) x 1.212 (if black) x 0.742 (if female), and for S(cr) (micromol/L) is GFR = 30849 x standardized S(cr)(-1.154) x age(-0.203) x 1.212 (if black) x 0.742 (if female) [GFR in mL x min(-1) x (1.73 m(2))(-1)].


CONCLUSIONS
When the calibration of S(cr) methods is traceable to the S(cr) reference system, GFR should be estimated using the MDRD Study equation that has been reexpressed for standardized S(cr).
Levey
Andrew S
AS
Division of Nephrology, Tufts-New England Medical Center, Boston, MA 02111, USA.
Coresh
Josef
J
Greene
Tom
T
Marsh
Jane
J
Stevens
Lesley A
LA
Kusek
John W
JW
Van Lente
Frederick
F
D000465:Algorithms; D002138:Calibration; D002908:Chronic Disease; D019411:Clinical Laboratory Techniques / Q000592:standards; D003404:Creatinine / Q000097:blood* / Q000592:standards*; D005919:Glomerular Filtration Rate; D006801:Humans; D007201:Indicator Dilution Techniques; D007674:Kidney Diseases / Q000175:diagnosis* / Q000503:physiopathology; D013058:Mass Spectrometry; D011933:Reagent Kits, Diagnostic; D012015:Reference Standards; D044967:Serum
D011933:Reagent Kits, Diagnostic; D003404:Creatinine