GFR Calculator
| Formula | Result |
|---|---|
| MDRD 4-Variable Equation | -- mL/min/1.73 m² |
| CKD-EPI Formula | -- mL/min/1.73 m² |
| Mayo Quadratic Formula | -- mL/min/1.73 m² |
Chronic Kidney Disease Stages:
| Stage | GFR Value (mL/min/1.73 m²) |
|---|---|
| Normal | 90+ or above and no proteinuria |
| CKD1 | 90+ with evidence of kidney damage |
| CKD2 (Mild) | 60 to 89 with evidence of kidney damage |
| CKD3 (Moderate) | 30 to 59 |
| CKD4 (Severe) | 15 to 29 |
| CKD5 Kidney failure | Less than 15 |
MDRD: 175 × (Scr)^-1.154 × (Age)^-0.203 × 0.742 [if female] × 1.212 [if black]
Example:
A 60-year-old black female with Scr = 1.1 mg/dL:
GFR ≈ 175 × (1.1)^-1.154 × (60)^-0.203 × 0.742 × 1.212 ≈ 63.1 mL/min/1.73 m²
Understanding Your Glomerular Filtration Rate (GFR)
What Does GFR Tell You About Your Kidneys?
The glomerular filtration rate, or GFR, essentially measures how well your kidneys are filtering fluids. Think of it as a gauge of your kidney function. Generally speaking, a higher GFR number suggests your kidneys are working efficiently. On the other hand, a noticeable drop in your GFR could indicate that your kidneys aren’t functioning as they should, leading to less fluid being filtered over time. For individuals under 40, a typical GFR range is around 100 to 130 mL/min/1.73m² for men and 90 to 120 mL/min/1.73m² for women, adjusted for body surface area. It’s worth noting that after the age of 40, GFR naturally tends to decrease with each passing year. You can see average GFR ranges for different age groups in the table below.
Population Mean Estimated GFR
| Age | Mean Estimated GFR (mL/min/1.73 m2) |
| 20-29 | 116 |
| 30-39 | 107 |
| 40-49 | 99 |
| 50-59 | 93 |
| 60-69 | 85 |
| 70+ | 75 |
Chronic Kidney Disease and GFR Levels
A GFR reading above 60 mL/min/1.73m² is often considered adequate for most people and doesn’t automatically mean someone has chronic kidney disease (CKD). However, if there’s a significant decline in GFR compared to previous tests, it could be an early sign of kidney issues. Early diagnosis and treatment of kidney disease are crucial, as they can significantly increase the chances of preventing the need for dialysis later on. The table below outlines the GFR ranges associated with different stages of CKD. Keep in mind that diagnosing the stage of CKD involves considering other factors in addition to GFR.
| Stage | GFR Value (mL/min/1.73 m2) |
| Normal | 90+ or above and no proteinuria |
| CKD1 | 90+ with evidence of kidney damage |
| CKD2 (Mild) | 60 to 89 with evidence of kidney damage |
| CKD3 (Moderate) | 30 to 59 |
| CKD4 (Severe) | 15 to 29 |
| CKD5 Kidney failure | less than 15 |
How GFR is Measured
The most precise way to measure GFR involves tracking how quickly an external substance, like inulin, is removed from your bloodstream – a process called inulin clearance. Inulin is ideal for this because the kidneys filter it freely, and it isn’t metabolized, secreted, or absorbed by the body. However, this method requires a continuous IV infusion, multiple blood and urine samples collected at specific times, making it impractical for routine clinical use. Because of this, numerous formulas have been developed to estimate GFR. Many of these rely on creatinine clearance or estimations of creatinine clearance based on serum creatinine levels. Creatinine clearance, however, has a limitation: it’s influenced by muscle mass. Higher muscle mass can lead to higher serum creatinine levels for the same level of kidney filtration. This means the same serum creatinine value might indicate different kidney function levels in different people depending on their muscle mass. Additionally, the body actively secretes small amounts of creatinine, which means GFR calculated through creatinine clearance is often overestimated by about 10-20%. Despite these limitations, creatinine clearance remains a useful way to estimate GFR because it’s much easier to measure compared to inulin clearance. Below are three common formulas used to estimate GFR using serum creatinine.
- “Normal GFR,” The UK eCKD Guide, The Renal Association.
- Gaspari, F., Perico, N., Remuzzi, G. 1997. “Measurement of glomerular filtration rate.” Kidney International Supplements 63: S151-4. PMID 9407445.
- Hsu, C., Bansal, N. 2011. “Measured GFR as ‘Gold Standard’ – All that Glitters Is Not Gold?” Clinical Journal of the American Society of Nephrology 6(8): 1813-14. Doi:10.2215/CJN.06040611.