Glomerular Filtration Rate (GFR)
GFR (mL/min/1.73 m2) = 175 × (Scr)-1.154 × (Age)-0.203 × (0.742 if female) × (1.212 if African American)
The equation does not require weight or height variables because the results are reported normalized to 1.73 m2 body surface area, which is an accepted average adult surface area.
Scr = Serum Creatinine level
Reference:
Related Calculators:
More about the GFR Calculator and CKD Classification:
Glomerular Filtration Rate (GFR) is the most widely accepted indicator of kidney function. Estimating GFR allows clinicians to assess renal performance, stage chronic kidney disease (CKD), guide medication dosing, and make decisions about nephrology referral and long-term monitoring. Our GFR Calculator uses the MDRD (Modification of Diet in Renal Disease) Study equation, a clinically validated and widely used formula in nephrology.
The MDRD equation estimates GFR based on serum creatinine, age, sex, and race. Though newer formulas like CKD-EPI exist, MDRD remains frequently used due to its historical validation and adoption in many electronic health systems. It is particularly useful in patients with moderate to severe renal impairment (GFR < 60 mL/min/1.73 m²).
Understanding the MDRD Equation
The MDRD formula estimates GFR using the following variables:
- Serum creatinine (mg/dL)
- Age (years)
- Sex (male or female)
- Race (Black or non-Black)
GFR (mL/min/1.73 m²) = 175 × (Serum Creatinine)^–1.154 × (Age)^–0.203 × (0.742 if female) × (1.212 if Black)
Clinical Significance
Accurate estimation of GFR helps classify CKD into stages, ranging from early disease to end-stage renal failure. This classification informs surveillance strategies, lifestyle interventions, and decisions about when to refer to nephrology. Our calculator provides instant CKD stage classification according to established KDIGO guidelines.
CKD Stages Based on GFR
- Stage 1: GFR ≥ 90 (with evidence of kidney damage)
- Stage 2: GFR 60–89
- Stage 3a: GFR 45–59
- Stage 3b: GFR 30–44
- Stage 4: GFR 15–29
- Stage 5: GFR < 15 (Kidney failure)
Patients with CKD stage 3 or lower often remain asymptomatic. Early detection through routine labs and GFR estimation allows for interventions that can delay progression to dialysis or transplantation.
When to Use the GFR Calculator
This calculator is helpful for:
- Routine screening in patients with risk factors such as hypertension or diabetes
- Adjusting medication dosages, especially nephrotoxic agents
- Evaluating eligibility for radiological contrast use
- Tracking disease progression in known CKD patients
- Counseling patients on lifestyle changes and referrals
Comparison with CKD-EPI and Other Equations
While the MDRD formula is reliable, the CKD-EPI equation has been shown to perform better at higher GFR levels. However, MDRD still holds utility in patients with known CKD, and many laboratories continue to report it alongside serum creatinine. In practice, both may be used depending on context, available software, and institutional protocols.
Limitations of GFR Estimation
Estimated GFR equations, including MDRD, are not accurate in patients with rapidly changing kidney function, extremes of muscle mass (e.g., bodybuilders or cachexia), or in the setting of acute kidney injury (AKI). In such cases, direct GFR measurement or alternative biomarkers like cystatin C may be more appropriate.
Additional Considerations
Our GFR Calculator offers an efficient way to screen and monitor kidney function in both inpatient and outpatient settings. It should be used in conjunction with urine testing, clinical history, and imaging when indicated. For example, a patient with a GFR of 55 may still be considered stage 3a CKD even without symptoms, emphasizing the importance of lab interpretation in clinical context.
In radiology, accurate GFR estimation is also critical before administering iodinated contrast agents. A GFR under 30 typically contraindicates contrast use due to the risk of contrast-induced nephropathy, unless benefits outweigh the risks and preventative measures are taken.
This tool complements related nephrology resources, such as our adrenal washout CT calculator or renal trauma radiology guidelines, by supporting kidney-related decision-making across disciplines.
References and Guidelines
Our GFR calculator aligns with KDIGO 2012 Clinical Practice Guidelines for the Evaluation and Management of Chronic Kidney Disease. It is designed to support clinical workflows, enable early detection, and encourage timely referral to nephrology when appropriate.
