When Not To Use the MDRD

The MDRD Study Equation Is Not for All Patients
Although an excellent tool for assessing kidney function, eGFR derived from the Modification of Diet in Renal Disease (MDRD) Study equation may not be suitable for all populations. MDRD-based estimates of GFR, like all creatinine-based estimates of kidney function (e.g., Cockcroft-Gault, reciprocal of serum creatinine), are only useful when renal function is stable; serum creatinine values obtained while kidney function is changing will not provide accurate estimates of kidney function.

Additionally, the equation is not recommended for use with:

• Nonadults. This includes all individuals under the age of 18. The Schwartz equation should be used to estimate GFR for infants, toddlers, children, and teens under age 18. 
• Individuals with unstable creatinine concentrations. This includes pregnant women; patients with serious co-morbid conditions; and hospitalized patients, particularly those with acute renal failure. The MDRD Study equation should be used only for patients with stable creatinine concentrations.
• Persons with extremes in muscle mass and diet. This includes, but is not limited to, individuals who are amputees, paraplegics, bodybuilders, or obese; patients who have a muscle-wasting disease or a neuromuscular disorder; and those suffering from malnutrition, eating a vegetarian or low-meat diet, or taking creatine dietary supplements.

Application of the equation to these patient groups may lead to errors in GFR estimation¹. GFR estimating equations have poorer agreement with measured GFR for ill hospitalized patients² and for people with near normal kidney function³ than for the patients in the MDRD Study.

As noted above, providers should exercise judgment regarding clinical status when presented with an MDRD Study-derived eGFR for a patient with an unstable creatinine level or other condition for which the equation is not suitable. Providers may not understand that estimating equations like the MDRD are derived from large populations of patients and provide the best estimate of mean GFR for a group of people of a certain age race, gender, and serum creatinine value. Thus, the reported eGFR is the best estimate of a patient’s GFR; it is not the patient’s actual GFR.

References

1. Myers GL, Miller WG, Coresh J, Fleming J, Greenberg N, Greene T, Hostetter T, Levey AS, Panteghini M, Welch M, Eckfeldt JH. Recommendations for improving serum creatinine measurement: a report from the laboratory working group of the National Kidney Disease Education Program. Clinical Chemistry. 2006;52:5–18.

2. Poggio ED, Nef PC, Wang X, Greene T, Van Lente F, Dennis VW, Hall PM. Performance of the Cockcroft-Gault and modification of diet in renal disease equations in estimating GFR in ill hospitalized patients. American Journal of Kidney Disease. 2005;46(2):242–252.

3. Poggio ED, Wang X, Greene T, Van Lente F, Hall PM. Performance of the modification of diet in renal disease and Cockcroft-Gault equations in the estimation of GFR in health and in chronic kidney disease. Journal of the American Society of Nephrology. 2005;16(2):459–466.