GFR计算器（肾小球滤过率计算器）
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What is Glomerular Filtration Rate (GFR)?
Glomerular filtration rate (GFR) is a test used to check how well your kidneys are working. Specifically, it estimates how much blood passes through the glomeruli (tiny filters in your kidneys) each minute. GFR is the best overall indicator of kidney function.
Your kidneys filter waste and extra fluid from your blood. As kidney disease gets worse, the GFR number decreases, indicating declining kidney function. Doctors use GFR to diagnose and monitor kidney disease, determine its severity, and plan treatment.
The normal GFR range for adults below age 40 is 100-130 mL/min/1.73m² for men and 90-120 mL/min/1.73m² for women. GFR naturally decreases with age, even in the absence of kidney disease.
GFR Calculation Formulas
MDRD Formula
The MDRD (Modification of Diet in Renal Disease) Study equation is commonly used to estimate GFR in adults. It takes into account serum creatinine, age, gender, and race.
$$\text{GFR} = 175 \times (\text{SCr})^{-1.154} \times (\text{age})^{-0.203} \times (0.742 \text{ if female}) \times (1.212 \text{ if Black})$$
CKD-EPI Formula
The CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation is more accurate than MDRD, especially at higher GFR values. It's now the preferred formula for most adults.
Black Female
If SCr < 0.7 mg/dL:
$$\text{GFR} = 166 \times (\text{SCr}/0.7)^{-0.329} \times 0.993^{\text{age}}$$
If SCr > 0.7 mg/dL:
$$\text{GFR} = 166 \times (\text{SCr}/0.7)^{-1.209} \times 0.993^{\text{age}}$$
Black Male
If SCr < 0.9 mg/dL:
$$\text{GFR} = 163 \times (\text{SCr}/0.9)^{-0.411} \times 0.993^{\text{age}}$$
If SCr > 0.9 mg/dL:
$$\text{GFR} = 163 \times (\text{SCr}/0.9)^{-1.209} \times 0.993^{\text{age}}$$
Non-Black Female
If SCr < 0.7 mg/dL:
$$\text{GFR} = 144 \times (\text{SCr}/0.7)^{-0.329} \times 0.993^{\text{age}}$$
If SCr > 0.7 mg/dL:
$$\text{GFR} = 144 \times (\text{SCr}/0.7)^{-1.209} \times 0.993^{\text{age}}$$
Non-Black Male
If SCr < 0.9 mg/dL:
$$\text{GFR} = 141 \times (\text{SCr}/0.9)^{-0.411} \times 0.993^{\text{age}}$$
If SCr > 0.9 mg/dL:
$$\text{GFR} = 141 \times (\text{SCr}/0.9)^{-1.209} \times 0.993^{\text{age}}$$
Mayo Quadratic Formula
The Mayo Quadratic Formula tends to be more accurate for people with normal or near-normal kidney function.
If SCr < 0.8 mg/dL, use 0.8 mg/dL for SCr
$$\text{GFR} = e^{(1.911 + 5.249/\text{SCr} - 2.114/\text{SCr}^2 - 0.00686 \times \text{age} - (0.205 \text{ if female}))}$$
Schwartz Formula (for Children)
The Schwartz formula is specifically designed for children and adolescents, taking into account height and serum creatinine.
$$\text{GFR} = 0.413 \times \text{height(cm)} / \text{SCr}$$
Chronic Kidney Disease (CKD) Stages
| Stage | GFR Range (mL/min/1.73m²) | Description |
|---|---|---|
| Normal | ≥ 90 | Normal kidney function |
| CKD Stage 1 | ≥ 90 (with evidence of kidney damage) | Normal GFR with evidence of kidney damage |
| CKD Stage 2 (Mild) | 60-89 | Mild decrease in kidney function |
| CKD Stage 3 (Moderate) | 30-59 | Moderate decrease in kidney function |
| CKD Stage 4 (Severe) | 15-29 | Severe decrease in kidney function |
| CKD Stage 5 (Kidney Failure) | < 15 | Kidney failure, may require dialysis or transplant |
Source: National Kidney Foundation
Age-Related GFR Reference Values
GFR naturally decreases with age, even in healthy individuals. Below are the population mean estimated GFR values by age range:
| Age Range | Mean GFR (mL/min/1.73m²) |
|---|---|
| 20-29 | 116 |
| 30-39 | 107 |
| 40-49 | 99 |
| 50-59 | 93 |
| 60-69 | 85 |
| 70+ | 75 |
Frequently Asked Questions
What is a good GFR for my age?
GFR naturally decreases with age. For adults under 40, a normal GFR is typically above 90 mL/min/1.73m². For those over 60, a GFR of 75 or above may be considered normal. The table in the Age Reference section provides more specific guidance.
How accurate are GFR estimates?
GFR estimates from these formulas are generally within 30% of the actual GFR as measured by more invasive methods. Factors like extreme muscle mass, malnutrition, pregnancy, or certain medications can affect the accuracy of the estimates.
What should I do if my GFR is low?
If your calculated GFR is below 60 mL/min/1.73m², consult with a healthcare provider. A low GFR may indicate kidney disease, but a single calculation is not sufficient for diagnosis. Your doctor will likely recommend additional tests.
How can I improve my GFR?
While you cannot directly increase your GFR, you can help protect your kidney function by: controlling blood pressure and blood sugar, maintaining a healthy weight, exercising regularly, avoiding smoking, limiting alcohol consumption, and avoiding nephrotoxic medications when possible.
How often should GFR be measured?
For individuals with known kidney disease, GFR should be measured as often as recommended by their healthcare provider, typically every 3-12 months depending on the stage of kidney disease. For those at risk of kidney disease, annual testing may be appropriate.
Medical Disclaimer
This calculator is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.
References
- Levey AS, Stevens LA, Schmid CH, et al. A new equation to estimate glomerular filtration rate. Ann Intern Med. 2009;150(9):604-612.
- Schwartz GJ, Muñoz A, Schneider MF, et al. New equations to estimate GFR in children with CKD. J Am Soc Nephrol. 2009;20(3):629-637.
- National Kidney Foundation. K/DOQI clinical practice guidelines for chronic kidney disease: evaluation, classification, and stratification. Am J Kidney Dis. 2002;39(2 Suppl 1):S1-S266.