MDRD GFR Calculator

The Modification of Diet in Renal Disease (MDRD) Study Equation is a formula developed in 1999 to estimate glomerular filtration rate (eGFR) from routinely available laboratory and patient variables. The simplified 4-variable version — using serum creatinine, age, sex, and race — became the most widely deployed eGFR equation in the 2000s and remains embedded in many laboratory information systems worldwide. GFR is the volume of plasma filtered by the glomeruli per unit time, normalised to a standard body surface area of 1.73 m². It is the cornerstone metric for staging Chronic Kidney Disease (CKD) and guides decisions about drug dosing, imaging contrast safety, and referral thresholds. The original MDRD study enrolled 1,628 adults with established CKD (mean GFR ~40 mL/min/1.73m²). Because the study population had moderate-to-severe kidney disease, the 4-variable equation systematically underestimates GFR at values above 60 mL/min/1.73m², where it cannot reliably distinguish normal from mildly impaired function. For this reason, many laboratories now report results as '>60' or '>90' rather than a precise figure when the MDRD estimate exceeds these thresholds. Despite being largely superseded by CKD-EPI 2021 for general use, MDRD retains a role in research (as the equation used in most historical CKD outcome studies), in certain laboratory systems that have not updated their reporting platforms, and in specific patient populations where its validation data remain applicable.

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1. 1Collect serum creatinine (Scr) in mg/dL, patient age in years, sex (male/female), and self-reported race (Black/non-Black).
2. 2Start with the constant 175 — this replaces the original 186 after IDMS (isotope dilution mass spectrometry) creatinine standardisation in 2005.
3. 3Raise Scr to the power of -1.154: higher creatinine means lower GFR, and the relationship is non-linear.
4. 4Raise Age to the power of -0.203: GFR declines with age; older patients produce less creatinine from lower muscle mass, so the age correction prevents overestimation.
5. 5Multiply by 0.742 if the patient is female: women have lower muscle mass and generate less creatinine per unit GFR than men.
6. 6Multiply by 1.212 if the patient self-identifies as Black: historical data suggested higher average muscle mass and creatinine generation in this group, though this race coefficient is now scientifically and ethically contested.
7. 7The result is eGFR in mL/min/1.73m². Values above 60 should be interpreted with caution as the equation loses accuracy in that range.

• !Using MDRD to report a precise GFR when the result is above 60 — values in this range should be reported as '>60' because the equation is not validated there.
• !Forgetting to check if the laboratory uses IDMS-standardised creatinine — older assays require the original constant of 186, not 175.
• !Applying the Black race coefficient automatically without patient consent or clinical reflection — this practice is now discouraged by KDIGO and most nephrology societies.
• !Using MDRD instead of Cockcroft-Gault for drug dosing — many pharmacokinetic studies and prescribing references are based on measured creatinine clearance, not BSA-normalised eGFR.
• !Interpreting a single low eGFR as CKD — CKD requires GFR below 60 (or markers of kidney damage) persisting for more than 3 months.
• !Applying MDRD in acute kidney injury — creatinine is not at steady state during AKI, making all eGFR formulas unreliable.