MDRD Equation Explained
The earlier eGFR equation, still widely reported.
Medically reviewed by Dr. Rishi Kumar Kafle, MBBS, MD, FASN · Last reviewed June 2026
The MDRD Study equation estimates eGFR in mL/min/1.73m². The IDMS-traceable 4-variable form is 175 × Scr^−1.154 × age^−0.203 × (0.742 if female), published in 1999 and re-expressed for standardised creatinine in 2006. We apply it race-free.
Every Term Defined
Each factor is a power of one input, so the equation is a product of three scaled terms and an optional sex adjustment. The negative exponents mean eGFR falls as creatinine and age rise.
| Term | Value | Role |
|---|---|---|
| Scaling constant | 175 | IDMS-traceable constant (was 186 before standardisation) |
| Serum creatinine | Scr^−1.154 | higher creatinine lowers eGFR |
| Age | age^−0.203 | eGFR falls gradually with age |
| Female factor | × 0.742 | adjusts for lower muscle mass |
The original 1999 equation used a constant of 186 and a Black-race factor of 1.212. The constant became 175 when creatinine assays were standardised to isotope-dilution mass spectrometry (IDMS) in 2006, and we omit the race coefficient entirely. Convert your lab value with the creatinine unit converter if it is reported in µmol/L.
A Worked Example
For a 60-year-old man with a serum creatinine of 1.5 mg/dL: 1.5^−1.154 ≈ 0.628, 60^−0.203 ≈ 0.434, and there is no female factor. Multiplying 175 × 0.628 × 0.434 gives an eGFR of about 48 mL/min/1.73m², placing the patient in CKD stage G3a. The same inputs in a woman would be multiplied by 0.742 for roughly 35 mL/min/1.73m².
History and Derivation
MDRD was derived from the Modification of Diet in Renal Disease study, a cohort with reduced kidney function. That sampling is the root of its main weakness: the model was fit on patients who mostly had GFR below 60, so it is accurate there but underestimates higher, near-normal values. The equation was first published in 1999 with a constant of 186 and a Black-race factor of 1.212. Two changes followed: in 2006 the constant was lowered to 175 when laboratories adopted IDMS-standardised creatinine assays, and more recently the race factor has been dropped in line with the move to race-free estimation. This site applies the IDMS, race-free form.
How to Read the Result
Like any eGFR, the MDRD output maps to the KDIGO CKD categories — G1 at 90 or above, G2 at 60–89, G3a at 45–59, G3b at 30–44, G4 at 15–29, and G5 below 15. The important caveat is that MDRD is not reliable above 60: many laboratories that report MDRD simply state “eGFR > 60” rather than a precise number, because the equation cannot be trusted to distinguish, say, 75 from 95. Use it to confirm and stage reduced function, not to rule out early disease — switch to CKD-EPI 2021 for that. See CKD stages for how the categories combine with albuminuria.
When You Will Still See MDRD
Despite being superseded, MDRD remains common in practice. Older medical records, legacy laboratory information systems, and some published reference ranges still use it, so clinicians need to recognise an MDRD value and know its near-normal underestimate. When a patient's record shows an MDRD eGFR alongside a newer CKD-EPI value, the two will agree closely at low GFR and diverge as function approaches normal — the CKD-EPI figure being the more accurate of the two. For children, neither adult equation applies; use the bedside Schwartz equation.
Strengths and Limitations
MDRD performs reasonably below an eGFR of 60 and is still printed by many laboratories, which is its practical strength. Its limitation is the systematic underestimation of higher GFR — it should not be used to confirm normal kidney function — which is why CKD-EPI 2021 is now preferred. Like all creatinine equations it also assumes a steady state and average muscle mass. Try the MDRD calculator or compare directly on MDRD vs CKD-EPI.
MDRD vs Creatinine Clearance
MDRD estimates GFR for staging; for drug dosing, use Cockcroft–Gault creatinine clearance instead, because dosing thresholds were validated against it — see CrCl vs eGFR.