Glomerular Filtration Rate (GFR) Calculator
Calculate your estimated GFR using serum creatinine levels with the CKD-EPI equation
Your GFR Results
Understanding Glomerular Filtration Rate (GFR) and Why Creatinine Matters
The glomerular filtration rate (GFR) is the gold standard for assessing kidney function. It measures how much blood passes through the glomeruli (tiny filters in the kidneys) each minute. Your GFR helps determine if you have kidney disease and at what stage.
Why Creatinine is Used to Estimate GFR
Creatinine is a waste product produced by muscle metabolism. Healthy kidneys efficiently filter creatinine from the blood, maintaining stable levels. When kidney function declines:
- Creatinine builds up in the blood
- GFR decreases proportionally
- The ratio becomes a reliable indicator of kidney health
The CKD-EPI equation (Chronic Kidney Disease Epidemiology Collaboration) is the most accurate formula for estimating GFR from creatinine levels, accounting for:
- Serum creatinine concentration
- Age (kidney function naturally declines with age)
- Biological sex (women typically have lower creatinine levels)
- Race (historically included as African Americans often have higher muscle mass)
| Stage | GFR (mL/min/1.73m²) | Description | Clinical Action |
|---|---|---|---|
| 1 | >90 | Normal kidney function | Maintain healthy lifestyle |
| 2 | 60-89 | Mildly reduced | Monitor for progression |
| 3a | 45-59 | Mild to moderate reduction | Evaluate and treat complications |
| 3b | 30-44 | Moderate to severe reduction | Prepare for kidney replacement |
| 4 | 15-29 | Severe reduction | Plan for dialysis/transplant |
| 5 | <15 | Kidney failure | Dialysis or transplant required |
Limitations of Creatinine-Based GFR Estimation
While creatinine is the most common marker, it has some limitations:
| Factor | Effect on GFR Estimation | Alternative Marker |
|---|---|---|
| Muscle mass | Low muscle mass may overestimate GFR | Cystatin C |
| Diet | High meat intake temporarily increases creatinine | 24-hour urine collection |
| Medications | Some drugs affect creatinine secretion | Iohexol clearance |
| Acute changes | Creates lag in detecting rapid kidney changes | Serum cystatin C |
When to See a Doctor
Consult a healthcare provider if you:
- Have a GFR <60 for 3+ months (possible CKD)
- Experience sudden GFR drops (>25% in short period)
- Have symptoms like fatigue, swelling, or frequent urination
- Have risk factors (diabetes, hypertension, family history)
Regular GFR monitoring is crucial for:
- People with diabetes or high blood pressure
- Those with a family history of kidney disease
- Individuals over age 60
- Patients taking nephrotoxic medications
Frequently Asked Questions
Can GFR fluctuate daily?
Yes, GFR can vary slightly due to hydration status, diet, and physical activity. However, significant fluctuations may indicate kidney problems.
Is a high GFR good?
While high GFR (>120) might seem beneficial, it can indicate hyperfiltration – a risk factor for future kidney damage, especially in diabetics.
How accurate is the CKD-EPI equation?
The CKD-EPI equation is about 10-20% more accurate than older formulas like MDRD, particularly at higher GFR levels (>60).
Can I improve my GFR?
Lifestyle changes can help preserve kidney function:
- Control blood pressure (<130/80 mmHg)
- Manage blood sugar (HbA1c <7% for diabetics)
- Reduce protein intake if advised
- Stay hydrated but avoid excessive fluids
- Exercise regularly (150+ mins/week)
- Avoid NSAIDs and nephrotoxic drugs