CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) Calculator
CKD-EPI (2021) eGFR Calculator
What is the Glomerular Filtration Rate (GFR)?
The Glomerular Filtration Rate (GFR) measures how quickly fluid is filtered by the kidneys and serves as an indicator of kidney function. An increase in GFR generally indicates healthy kidney function. A significant decrease in GFR indicates that the kidneys are not working efficiently, causing less fluid to be filtered in a given time. The normal GFR range, adjusted for body surface area, is 100 to 130 mL/min/1.73m² in men and 90 to 120 mL/min/1.73m² in women under the age of 40. After the age of 40, GFR gradually decreases with age. The table below shows the population average estimated GFR in different age groups.
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 |
Stages of Chronic Kidney Disease (CKD)
A GFR above 60 mL/min/1.73m² is usually sufficient for most people and does not automatically indicate chronic kidney disease (CKD). However, a significant decrease in GFR compared to previous tests may be an early sign of kidney problems. Early diagnosis and treatment of kidney disease can improve the chances of avoiding dialysis. The table below presents the GFR ranges corresponding to the different CKD stages. These stages take into account other factors in addition to GFR.
| Stage | GFR Value (mL/min/1.73 m²) |
|---|---|
| Normal | 90+ 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 |
Measuring GFR
The most accurate method of measuring GFR involves tracking how quickly a foreign substance such as inulin is removed from the blood, known as inulin clearance. Inulin is freely filtered by the kidneys and is not metabolized or secreted, making it ideal for measuring GFR. This process requires continuous IV infusions, multiple blood and urine samples, and precise timing, making it less practical for routine use.
As a result, several formulas have been developed to estimate GFR, many of which are based on creatinine clearance or serum creatinine levels. However, creatinine clearance can be affected by muscle mass; people with more muscle mass have higher serum creatinine for the same kidney function. In addition, the body excretes little creatinine, so the GFR estimated by creatinine clearance is often 10-20% higher than the actual GFR. Despite these limitations, creatinine clearance remains a convenient and reliable estimate of GFR compared to insulin clearance. The following three formulas are commonly used to estimate GFR from serum creatinine.
CKD-EPI Formula
Black Female
If SCr falls below 0.7
GFR = 166 × (SCr/0.7)⁻⁰·³²⁹ × 0.993^age
If SCr rises above 0.7
GFR = 166 × (SCr/0.7)⁻¹·²⁰⁹ × 0.993^age
Black Male
If SCr remains below 0.9
GFR = 163 × (SCr/0.9)⁻⁰·⁴¹¹ × 0.993^age
If SCr rises above 0.9
GFR = 163 × (SCr/0.9)⁻¹·²⁰⁹ × 0.993^age
Non-Black Female
If SCr remains below 0.7
GFR = 144 × (SCr/0.7)⁻⁰·³²⁹ × 0.993^age
If SCr exceeds 0.7
GFR = 144 × (SCr/0.7)⁻¹·²⁰⁹ × 0.993^age
Non-black male
If SCr is less than 0.9
GFR = 141 × (SCr/0.9)⁻¹·⁴¹¹ × 0.993^age
If SCr is greater than 0.9
GFR = 141 × (SCr/0.9)⁻¹·²⁰⁹ × 0.993^age
Components of the CKD-EPI equation
To apply the CKD-EPI formula, you need a person’s serum creatinine value, gender, age, and race. A simple blood test can measure serum creatinine levels. Then, you can calculate GFR using the following equation:
GFR (ml/min/1.73 m²) = 141 × min(Serum creatinine/κ, 1)^α × max(Serum creatinine/κ, 1)^-1.209 × 0.993^age × 1.018 [if female] × 1.159 [if black]
Where
- Serum creatinine refers to the creatinine level in the bloodstream (expressed in mg/dL)
- κ is a fixed value based on gender (0.7 for women and 0.9 for men)
- α is a constant that varies with gender and age (0.329 for women, -0.411 for men under 70, and -0.329 for men 70 and older)
- Age refers to the person’s age in years
Limitations of the 2021 CKD-EPI eGFRcr Equation
Although both creatinine and cystatin C provide more reliable estimates, cystatin C testing is not commonly performed in routine practice. For this reason, the 2021 CKD-EPI eGFRcr formula will remain the most widely used method for now. Therefore, it is important to understand where this equation falls short. Estimated GFR calculated with the 2021 CKD-EPI eGFRcr may show reduced accuracy when compared with the 2021 CKD-EPI eGFRcr-cys, the 2012 CKD-EPI eGFRcys, and the older 2009 race-based CKD-EPI equations. 1,2,3,4 On average, the 2021 CKD-EPI eGFRcr reads GFR values approximately 4% higher for non-Black individuals and approximately -4% lower for Black individuals.
Healthcare teams can decide how to manage these small changes in different eGFR calculations based on each patient’s situation. This approach helps guide clinical choices, including medication dosage and eligibility for a kidney transplant list.
FAQs: Frequently Asked Questions
Q1. What eGFR is considered abnormal in CKD-EPI?
An eGFR is considered abnormal when a CKD-EPI reading falls below the normal range for healthy kidneys. Kidney stages help show how much eGFR has declined.
Test results and stages of CKD
Stage 1 (G1) – Your eGFR remains above 90 ml/min, but other tests show early kidney damage.
Stage 2 (G2) – Your eGFR remains between 60 and 89 ml/min, with other signs that suggest kidney damage.
Stage 3a (G3a) – Your eGFR remains between 45 and 59 ml/min.
Stage 3b (G3b) – Your eGFR remains between 30 and 44 ml/min.
Q2. What is Stage 1 CKD-EPI?
Stage 1 CKD means that your estimated glomerular filtration rate (eGFR) is 90 or higher, but your urine test shows protein loss. Even though your kidneys are filtering normally, protein in your urine confirms stage 1 CKD. So stage 1 CKD is diagnosed when your eGFR is 90 or higher with protein in your urine.
Q3. How can I improve my CKD-EPI?
High blood pressure and diabetes are common causes of CKD, so you should control both to protect your kidneys. You can also support kidney health by: choosing low-salt foods, reducing your intake of packaged foods high in sodium, and following a low-salt diet every day.
Q4. What is CKD-EPI in blood tests?
The CKD-EPI blood test helps estimate your glomerular filtration rate (eGFR), which shows how well your kidneys are clearing waste. It checks your blood for creatinine or cystatin C and then uses your age, gender, and sometimes body size to calculate kidney function. A low eGFR level means your kidneys are not filtering as well as they should.
