MDRD GFR Equation

Modification of Diet in Renal Disease (MDRD) equation is used to measure kidney function in patients with stable, chronic kidney disease (not acute) to determine degree or presence of decreased kidney function. This equation use serum creatinine to measure creatinine clearance as a proxy to estimate glomerular filtration rate(GFR). The MDRD equation performs equally to the newer CKD-EPI Equation in patients with GFR of < 60 ml/min/1.73 m² and performs superiorly to the Cockcroft-Gault Equation. To accommodate recent standardization of creatinine assays over IDMS, the MDRD equation has been revised (new constant of 186 from 175). However, the literature does not suggest that the revised version is significantly better. Of note, the same authors of MDRD also developed the newer CKD-EPI equations, which may be more accurate at a broader range of estimated GFR than the MDRD equations.

Some of the CKD-EPI equations include adjustments based on race. However, adjustments base on race appear to be controversial and the pros/cons of adjustments ought to be part of a shared decision-making approach between the clinician and the patient. For more information on the topic of eGFR equations and race, NephJC (FitzGerald, 2019) provides an excellent primer on the subject.

The Modification of Diet in Renal Disease (MDRD) GFR formula was derived and validated in patients from the MDRD cohort by Levey et al (1999). 

• Most useful in patients with impaired kidney function (eGFR < 60 ml/min/1.73 m²).
• Not been validated in patients > 70 years old, but widely used in these patients.
• Additional adjustments can be made for certain populations.
• The formula in this evaluation uses the new MDRD version (new constant of 186) to accommodate recent standardization of creatinine assays over IDMS (Levey, 2006)
• The formula also offers an optional adjustment based on black race. Race may or may not provide a better estimate of GFR. Refer to the section (Usage) below for more information.
• Despite improvements to the MDRD equation, it may significantly underestimate GFR in patients with a GFR > 60 ml/min/1.73 m².

Formula

GFR = 175 x Serum Cr^(-1.154) x Age^(-0.203) x (1.212 if black) x (0.742 if female)

Chronic Kidney Disease (CKD) Staging

Source: KIDGO 2012 Clinical Practice Guidelines

Abbreviations

• Serum Cr = serum creatinine (mg/dL)
• GFR = glomerular filtration rate (ml/min/1.73 m²)

For use in patients with stable, chronic kidney disease to measure kidney function to estimate GFR, and not accurate for acute renal failure.

Adjustments based on race

Adjustments base on race appear to be controversial, and the pros/cons of adjustments ought to be part of a shared decision-making approach between the clinician and the patient. For more information on the topic of eGFR equations and race, NephJC (FitzGerald, 2019) provides an excellent primer on the subject.