What is Glomerular Filtration Rate?
GFR measures how much blood your kidneys filter per minute, expressed in mL/min/1.73m² (normalized to body surface area). It is the primary indicator of kidney function and is used to diagnose and stage chronic kidney disease (CKD).
GFR Formulas
CKD-EPI 2021 (Recommended)
The current standard from KDIGO guidelines. This race-free equation was adopted after the 2021 NKF-ASN task force recommendation:
eGFR = 142 × min(SCr/κ, 1)α × max(SCr/κ, 1)−1.200 × 0.9938Age × (1.012 if female)
Where κ = 0.7 (female) or 0.9 (male), and α = −0.241 (female) or −0.302 (male).
MDRD (Modification of Diet in Renal Disease)
The 4-variable MDRD formula is less accurate above 60 mL/min but still widely used:
eGFR = 175 × SCr−1.154 × Age−0.203 × (0.742 if female)
Cockcroft-Gault
The oldest formula, still used for drug dosing. Requires body weight and is not normalized to body surface area:
CrCl = ((140 − Age) × Weight) / (72 × SCr) × (0.85 if female)
Bedside Schwartz (Pediatric)
For children under 18:
eGFR = 0.413 × Height(cm) / SCr
CKD Stages
| Stage | GFR (mL/min/1.73m²) | Description |
|---|---|---|
| G1 | ≥ 90 | Normal or high function |
| G2 | 60–89 | Mildly decreased |
| G3a | 45–59 | Mild to moderate decrease |
| G3b | 30–44 | Moderate to severe decrease |
| G4 | 15–29 | Severely decreased |
| G5 | < 15 | Kidney failure (dialysis or transplant may be needed) |
Factors Affecting GFR
- Age: GFR naturally declines about 1 mL/min/year after age 30
- Diet: High protein intake temporarily increases GFR; creatine supplements raise serum creatinine without kidney damage
- Muscle mass: Muscular individuals may have higher creatinine, underestimating GFR
- Medications: NSAIDs, ACE inhibitors, and some antibiotics can affect GFR
- Hydration: Dehydration temporarily lowers GFR
When to See a Doctor
This calculator provides estimates only and should not replace medical advice. See a healthcare provider if your estimated GFR is below 60, or if you have symptoms like persistent fatigue, swelling, changes in urination, or foamy urine.