62.9
mL/min/1.73m²
2
70
%
62.9
mL/min/1.73m²
2
70
%
The MDRD GFR Calculator uses the Modification of Diet in Renal Disease study equation to estimate glomerular filtration rate. The 4-variable MDRD equation, re-expressed for IDMS-standardized creatinine assays, calculates eGFR from serum creatinine, age, and sex. While largely superseded by the CKD-EPI equation for routine clinical use, the MDRD equation remains relevant because of its extensive validation history, its widespread use in published research, and its continued reference in many clinical guidelines and drug dosing protocols.
The MDRD study, a landmark clinical trial that began in 1989, investigated the effect of dietary protein restriction and strict blood pressure control on the progression of chronic kidney disease. As part of the study, iothalamate clearance was measured in over 1,600 patients with CKD, providing a large dataset of gold-standard GFR measurements paired with clinical variables. The original 6-variable equation was later simplified to the 4-variable version using serum creatinine, age, sex, and race, and subsequently re-expressed for use with IDMS-traceable creatinine assays in 2006.
The 4-variable IDMS-traceable MDRD equation is: eGFR = 175 x Scr^(-1.154) x age^(-0.203) x 0.742 (if female). This version, presented here without the race coefficient for consistency with current recommendations to move toward race-free equations, provides reasonable accuracy for patients with established CKD (GFR below 60 mL/min/1.73m2). However, the MDRD equation systematically underestimates GFR in individuals with normal or near-normal kidney function, which led many laboratories to report MDRD results above 60 as simply greater than 60 rather than providing exact values.
The primary limitation of the MDRD equation compared to CKD-EPI is its poor performance at higher GFR values. In populations with normal or mildly reduced kidney function, MDRD underestimates GFR and may falsely classify individuals as having CKD Stage G3a when their true GFR is above 60. The CKD-EPI equation was developed specifically to address this limitation and provides more accurate estimates across the full range of GFR values. Current KDIGO guidelines recommend CKD-EPI over MDRD for routine clinical practice.
Despite these limitations, the MDRD equation has an established role in clinical research and epidemiology. Thousands of published studies have used MDRD-estimated GFR to define kidney function categories, establish CKD prevalence, and evaluate outcomes. Understanding and being able to calculate MDRD eGFR remains important for interpreting these studies and comparing results across different research contexts. Additionally, some institutional laboratory systems continue to report MDRD eGFR alongside or instead of CKD-EPI.
The transition from MDRD to CKD-EPI, and from CKD-EPI 2009 to CKD-EPI 2021 (without race), represents the evolving understanding of kidney function estimation. Each iteration has improved accuracy and equity in kidney disease assessment. Clinicians should be aware of which equation their laboratory uses and the implications for clinical decision-making, particularly near the GFR thresholds that define CKD stages and drug dosing categories.
The MDRD 4-variable IDMS-traceable equation calculates eGFR = 175 x Scr^(-1.154) x age^(-0.203) x 0.742 if female. Serum creatinine has an inverse exponential relationship with GFR (the -1.154 power). Age has a negative exponential effect reflecting declining GFR with aging. The female coefficient (0.742) accounts for lower creatinine generation from lower average muscle mass in women.
MDRD eGFR values below 60 mL/min/1.73m2 are considered reasonably accurate and correspond to CKD Stage G3 or worse. Values above 60 are unreliable and should not be used for precise GFR estimation; CKD-EPI is preferred for this range. The MDRD equation is most appropriate for patients with known CKD where the primary question is tracking disease progression rather than screening or initial diagnosis.
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eGFR of 41.2 mL/min/1.73m2 indicates CKD Stage G3b. This level requires close monitoring, nephrology referral, and drug dose adjustments for renally cleared medications.
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Results
MDRD eGFR of 71.1 likely underestimates true GFR. CKD-EPI would give a more accurate result in this range. This patient likely has normal kidney function.
The Modification of Diet in Renal Disease (MDRD) equation estimates GFR from serum creatinine, age, and sex. The 4-variable IDMS-traceable version is: eGFR = 175 x Scr^(-1.154) x age^(-0.203) x 0.742 if female. It was derived from iothalamate clearance measurements in approximately 1,600 patients with CKD.
The MDRD equation was developed in a population with established CKD (mean GFR ~40). It was not designed or validated for higher GFR values. At GFR above 60, MDRD systematically underestimates true GFR, potentially misclassifying healthy individuals as having kidney disease.
CKD-EPI 2021 is recommended by KDIGO as the preferred equation for clinical use. It is more accurate across the full GFR range, especially above 60. MDRD may still be encountered in older laboratory systems and published research. Use CKD-EPI for new clinical decisions.
IDMS (isotope dilution mass spectrometry) is the reference method for creatinine measurement. Modern standardized creatinine assays are calibrated (traceable) to this reference. The MDRD equation was re-expressed in 2006 to give accurate results with IDMS-traceable creatinine values, as older assays gave systematically higher readings.
The race coefficient (1.212 for Black patients) was based on observed higher creatinine levels in Black participants in the MDRD study, attributed to greater average muscle mass. It was removed following consensus that race is a social construct and its inclusion perpetuated disparities in kidney disease diagnosis and access to care.
Some older drug labels reference MDRD eGFR for dosing, but most pharmacokinetic studies used Cockcroft-Gault CrCl. When MDRD is specifically referenced, it should be used. Otherwise, Cockcroft-Gault is preferred for drug dosing and CKD-EPI for disease staging.
The equation was derived from the MDRD study, which enrolled 1,628 patients with CKD between 1989 and 1993. GFR was measured by 125-I-iothalamate clearance. Multiple regression analysis identified serum creatinine, age, sex, and race as the strongest predictors of measured GFR.
The original MDRD equation used 6 variables: serum creatinine, BUN, albumin, age, sex, and race. The simplified 4-variable version (dropping BUN and albumin) was found to perform nearly as well and is far more practical for clinical use, becoming the standard version used by laboratories.
MDRD performs poorly in healthy populations with normal GFR because it was developed in CKD patients. In screening settings, it overestimates the prevalence of CKD stage G3. The CKD-EPI equation was specifically developed to improve accuracy in populations with both normal and reduced GFR.
Creatinine assay standardization significantly affects eGFR calculations. Using the IDMS-traceable MDRD equation with a non-standardized (old Jaffe method) assay will overestimate GFR because non-standardized assays report higher creatinine values. Always confirm your laboratory uses IDMS-traceable creatinine and the corresponding MDRD equation version.
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