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.
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