Glomerular Filtration Rate (MDRD)

What the MDRD equation is and why it still appears

The MDRD (Modification of Diet in Renal Disease) equation estimates the glomerular filtration rate from serum creatinine and demographic data. It arose from the MDRD study, a clinical trial on diet in people with chronic kidney disease, and was published by Levey and colleagues in 1999.

In 2006, the same group re-expressed the four-variable version for creatinine calibrated by isotope dilution mass spectrometry (IDMS). The constant became 175. That is the version used in this calculator. The 2006 study included 1,628 patients with chronic kidney disease, with a mean measured GFR of 39.8 mL/min/1.73 m².

For years, MDRD was the standard equation on laboratory reports. Today, the National Kidney Foundation recommends CKD-EPI 2021, and the KDIGO 2024 guideline recommends not using race in the calculation. MDRD still appears on older reports, in studies and in dose adjustment protocols, so it is useful to know how to calculate it and compare it with the GFR by CKD-EPI 2021.

How to calculate GFR by MDRD in the calculator

The calculator asks for three inputs:

1. Serum creatinine, in mg/dL, greater than zero and up to 30 mg/dL.
2. Age, in years, from 18 to 120, because the equation was developed for adults. The tool uses only the whole number part: 72.6 years is entered as 72.
3. Sex: female (default option) or male.

The result is given in mL/min/1.73 m², as a whole number, as KDIGO 2024 recommends for reports, followed by the GFR G category. Values outside the accepted ranges produce an error message explaining what to correct.

The equation published in 2006 has a coefficient of 1.212 for Black people. The calculator does not apply it: KDIGO 2024 recommends not using race in GFR estimation, and the National Kidney Foundation and American Society of Nephrology task force recommended abandoning race-based equations. For that reason there is no question about race.

Before entering values, check that creatinine is in mg/dL (µmol/L ÷ 88.4, KDIGO 2024 factor) and that the laboratory uses an IDMS-traceable method. The constant 175 only applies to standardized creatinine.

Four-variable MDRD formula (IDMS version, 2006)

The calculator applies the four-variable MDRD equation re-expressed for standardized creatinine, described by Levey and colleagues in 2006.

eGFR = 175 × S_Cr^−1.154 × age^−0.203 × 0.742 [if female]

• eGFR: estimated glomerular filtration rate, in mL/min/1.73 m².
• S_Cr: standardized (IDMS) serum creatinine, in mg/dL.
• age: in years.
• 0.742: factor for female sex.
• Race: the published equation multiplied the result by 1.212 in Black people; that factor is not applied here, in line with KDIGO 2024.
• 175: constant of the version for standardized creatinine. The original four-variable version (2000), for non-standardized creatinine, used 186.

The structure differs from CKD-EPI. In MDRD, creatinine enters with a single exponent across the whole range, while CKD-EPI changes the exponent depending on whether creatinine is below or above a threshold. That difference explains much of MDRD's inaccuracy at higher filtration rates.

Worked example: creatinine of 1.2 mg/dL at age 60

Hypothetical case: serum creatinine of 1.2 mg/dL, age 60.

1. 1.2^−1.154 = 0.8102.
2. 60^−0.203 = 0.4356.
3. 175 × 0.8102 × 0.4356 = 61.8.

• Man: eGFR = 61.8, which on the report becomes 62 mL/min/1.73 m² (category G2).
• Woman: 61.76 × 0.742 = 45.8, which on the report becomes 46 mL/min/1.73 m² (category G3a).

The calculator returns 62 and 46 for these data.

Compare with CKD-EPI 2021 for the same creatinine and age: 69 for the man and 52 for the woman. The difference of 7 and 6 mL/min/1.73 m² illustrates what studies have shown: the equations diverge, and MDRD tends to underestimate filtration at higher values. In both sexes, the two equations agree on the category (G2 for the man, G3a for the woman), but the woman's MDRD value is close to the G3b limit.

How to understand the MDRD result

The calculator classifies eGFR using the categories of the KDIGO 2024 guideline. They are: G1 (90 or more), G2 (60 to 89), G3a (45 to 59), G3b (30 to 44), G4 (15 to 29) and G5 (less than 15 mL/min/1.73 m²). The category is applied to the whole number shown in the result.

MDRD calls for a specific precaution. The 2006 study warns that the sample included few patients with GFR above 90 and that the differences between measured and estimated GFR were larger when eGFR was 60 or more. The authors concluded that the equation gives reasonably accurate estimates in people with chronic kidney disease and measured GFR below 90. In practice, high MDRD values should be read as “60 or more”, not as an exact number; the calculator shows this warning when the result reaches 60.

The category alone does not diagnose chronic kidney disease. KDIGO 2024 requires an abnormality for at least three months and combines GFR with albuminuria. Spot urine protein can be assessed with the spot urine protein calculator. Interpretation is up to the healthcare professional.

Common errors and verification checklist

MDRD errors fall into those involving creatinine and those involving the version of the equation.

• Wrong version: applying 186 with standardized creatinine, or 175 with non-standardized creatinine, shifts all results.
• Creatinine in µmol/L in the mg/dL field: the result comes out close to zero.
• High value read as exact: above 60, inaccuracy increases.
• Use in acute kidney injury: creatinine is not stable and the estimate does not apply.
• Comparing MDRD from one report with CKD-EPI from another: the difference may be only in the equation, not in kidney function.
• Comparing with calculators that still apply the race factor: the 1.212 raises the result by 21%; this tool does not use that factor, in line with KDIGO 2024.

Checklist:

1. Creatinine in mg/dL, from an IDMS-traceable method?
2. Adult patient, with stable creatinine?
3. Is the version the 2006 one (175)?
4. Was the result compared with CKD-EPI 2021?
5. Was the category read together with albuminuria or proteinuria?

MDRD, CKD-EPI and creatinine clearance: comparison

The main difference between MDRD and CKD-EPI lies in performance at higher filtration rates. CKD-EPI 2009 was created by the same group of researchers to address that limitation, and the 2021 version removed the race variable.

In the 2006 study, 90% of MDRD estimates fell within 30% of measured GFR, compared with 60% for Cockcroft-Gault without bias correction. Creatinine clearance with 24-hour urine is another alternative, useful when estimates seem inconsistent, but subject to collection errors, according to KDIGO 2024.

Frequently asked questions about eGFR by the MDRD equation

References

1. Levey AS, Coresh J, Greene T, Stevens LA, Zhang YL, Hendriksen S, et al. Using standardized serum creatinine values in the modification of diet in renal disease study equation for estimating glomerular filtration rate. Ann Intern Med. 2006;145(4):247-54. View
2. Levey AS, Bosch JP, Lewis JB, Greene T, Rogers N, Roth D. A more accurate method to estimate glomerular filtration rate from serum creatinine: a new prediction equation. Modification of Diet in Renal Disease Study Group. Ann Intern Med. 1999;130(6):461-70. View
3. Levey AS, Stevens LA, Schmid CH, Zhang YL, Castro AF 3rd, Feldman HI, et al. A new equation to estimate glomerular filtration rate. Ann Intern Med. 2009;150(9):604-12. View
4. Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int. 2024;105(4S):S117-S314. View
5. Delgado C, Baweja M, Crews DC, Eneanya ND, Gadegbeku CA, Inker LA, et al. A unifying approach for GFR estimation: recommendations of the NKF-ASN Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Disease. J Am Soc Nephrol. 2021;32(12):2994-3015. View
6. National Kidney Foundation. CKD-EPI Creatinine Equation (2021). View