CKD-EPI 2021 vs MDRD: Which eGFR Equation Is More Accurate?
If you have compared kidney function results from different years, you may have noticed your eGFR changed even when your creatinine did not. That is because the formula used to estimate eGFR has evolved — from MDRD, to CKD-EPI 2009, to the current CKD-EPI 2021 equation. This article explains the differences and why CKD-EPI 2021 is now the recommended standard.
Our eGFR calculator uses the current CKD-EPI 2021 equation by default.
The three main equations
Over the past two decades, three creatinine-based equations have dominated kidney function estimation:
| Equation | Year | Key feature | Status today |
|---|---|---|---|
| MDRD | 1999 | 4-variable formula, included a race multiplier | Obsolete |
| CKD-EPI (2009) | 2009 | More accurate at high eGFR, still used race | Superseded |
| CKD-EPI (2021) | 2021 | Race-free, current recommended standard | Preferred |
What was MDRD?
The MDRD (Modification of Diet in Renal Disease) study equation, published in 1999, was the first widely adopted eGFR formula. It estimated GFR from serum creatinine, age, sex, and a race coefficient (multiplying the result for Black patients). It performed reasonably well in advanced kidney disease but systematically underestimated eGFR in the normal and high ranges, which sometimes led to over-diagnosis of early CKD.
CKD-EPI 2009: a better estimate
In 2009 the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation improved on MDRD. It was more accurate across the range, especially at eGFR above 60, and reduced the false-positive CKD diagnoses that MDRD produced in healthy people. Like MDRD, the 2009 version still included a race multiplier.
Why CKD-EPI 2021 removed race
In 2021, a joint task force from the National Kidney Foundation (NKF) and the American Society of Nephrology (ASN) recommended a new, race-free equation. The reasons:
- Race is a social construct, not a biological variable — using it in a medical formula reinforced health disparities.
- The original race coefficient assumed greater average muscle mass in Black patients, which did not apply uniformly and could delay diagnosis by making eGFR appear artificially higher.
- Large validation studies showed the race-free equation performed well across diverse populations and was more equitable.
The 2021 update also slightly improved calibration against measured GFR. See how to calculate eGFR for the full formula.
Practical impact on your numbers
Switching from an older equation to CKD-EPI 2021 shifts results in predictable ways:
- For many non-Black patients, eGFR may be slightly lower than under the 2009 race-based equation.
- For many Black patients, eGFR is now lower than under the old race-multiplied equation, which can lead to earlier CKD detection and timelier care.
These shifts are intentional and reflect a more accurate, equitable estimate — they do not mean your kidneys suddenly changed.
Which equation is most accurate?
For adults with stable kidney function, CKD-EPI 2021 is the most accurate and equitable creatinine-based equation available and is recommended by the NKF and ASN. Caveats:
- It is still an estimate, not a measured GFR.
- For extreme muscle mass, pregnancy, or acute kidney injury, accuracy drops — a cystatin C-based or combined equation may be better.
- For some drug dosing, labels still reference Cockcroft-Gault; see creatinine clearance vs eGFR.
What this means for your lab reports
Because laboratories adopt new equations at different times, the same creatinine value can produce a slightly different eGFR depending on which formula the lab uses. If your eGFR looks different from a prior year despite an unchanged creatinine, the equation change is the most likely explanation — not a sudden change in kidney function. Most labs now print the eGFR next to the creatinine value and may note the equation used. When tracking kidney health over years, compare creatinine trends alongside eGFR, and ideally use results from the same lab and equation. If you switch providers, ask which equation they use so you interpret small differences correctly rather than mistaking a calibration shift for real decline.
Common questions
Why did my eGFR change if my creatinine is the same? Because the lab or calculator switched equations (often to CKD-EPI 2021). Same creatinine + different formula = different eGFR.
Is MDRD still used? Rarely. Some older systems still display it, but current guidelines recommend CKD-EPI 2021.
Does removing race make eGFR less accurate? No — large studies show the race-free CKD-EPI 2021 equation performs comparably or better overall, while being more equitable.
Bottom line
CKD-EPI 2021 replaced both MDRD and CKD-EPI 2009 because it is more accurate at higher eGFR values and removes race from the calculation for greater equity. For everyday use, our free eGFR calculator applies the current 2021 equation, and you can learn more in our kidney function FAQ.
This article is for educational purposes only and is not medical advice. Always consult a qualified healthcare professional for diagnosis and treatment.