Glomerular filtration rate (eGFR)
The glomerular filtration rate (GFR) is the main measure of how well the kidneys work. The calculator estimates eGFR using the CKD-EPI equations — the method recommended by KDIGO (2024) — from creatinine and, when available, cystatin C, and it determines the CKD category with the associated risk and follow-up plan.
What GFR and CKD-EPI are
The glomerular filtration rate (GFR) is the volume of blood the kidneys clean per unit of time. It is the main measure of kidney function and of the stages of kidney failure. GFR is rarely measured directly (that is difficult), so it is estimated by calculation — hence “eGFR” (estimated GFR).
CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) is a modern set of equations for estimating the kidneys' filtration capacity. KDIGO (2024) recommends CKD-EPI as the most suitable screening method. The basic estimate uses creatinine; when cystatin C is available, the equations that include it are preferred — they are more accurate.
What's needed for the calculation
- Age and sex. They enter the CKD-EPI equations.
- Serum creatinine, µmol/L. A required value — the basic estimate is calculated from it.
- Cystatin C, mg/L — optional. If you have it, the calculator will additionally compute the more accurate equations (creatinine + cystatin C, and cystatin C).
eGFR calculator (CKD-EPI)
Enter your age, sex and creatinine (and cystatin C, if you have it) — the calculator will compute eGFR using the applicable CKD-EPI equations, determine the CKD category, the risk, the monitoring frequency and whether a nephrologist is needed. The calculation runs on the server.
CKD categories (KDIGO): ≥90 C1 · 60–89 C2 · 45–59 C3a · 30–44 C3b · 15–29 C4 · <15 C5.
How to read the result: CKD categories
The eGFR result is sorted into six categories (KDIGO). Each one sets the risk of progression, the frequency of monitoring and whether a nephrologist is needed:
| eGFR | Category | Risk | Nephrologist |
|---|---|---|---|
| ≥ 90 | C1 — optimal | Low | Not required |
| 60–89 | C2 — mildly decreased | Low | Not required |
| 45–59 | C3a — moderately decreased | Moderate | Not required |
| 30–44 | C3b — substantially decreased | Moderate | Recommended |
| 15–29 | C4 — severely decreased | Very high | Recommended |
| < 15 | C5 — kidney failure | Extremely high | Recommended |
Creatinine or cystatin C?
Creatinine is the most accessible marker, but it depends on muscle mass, diet and physical activity, so in some people it distorts the estimate. Cystatin C is almost independent of muscle mass, which is why equations that include it are more accurate. KDIGO advises: screen with creatinine, and when cystatin C is available, give preference to the estimates that include it. If you enter both values, the calculator will show all three results and determine the final category from the most accurate one (creatinine + cystatin C).
Why height and weight are not needed
The CKD-EPI equations give an eGFR that is already normalized to a standard body surface area (1.73 m²) — which is why the unit of measurement is “mL/min/1.73 m².” Height and weight do not enter these formulas. This distinguishes eGFR from the old creatinine clearance (Cockcroft–Gault), where weight is used.
Limitations and important caveats
- It is an estimate, not an exact measurement. eGFR is a calculated value; in borderline cases it is refined.
- A CKD diagnosis is not made from a single test. A persistent decrease in eGFR for ≥ 3 months is needed, along with consideration of albuminuria.
- Creatinine depends on muscle mass. In athletes, in wasting, or after amputations the creatinine-based estimate can be misleading — cystatin C is more accurate.
- Acute conditions distort the result. In acute kidney injury or dehydration the formula is less reliable.
- It does not replace an examination. The result is interpreted by a physician, taking your history into account.
Frequently asked questions
What does “mL/min/1.73 m²” mean?
It is the volume of blood (in mL) cleaned by the kidneys per minute, scaled to a standard body surface area of 1.73 m². The normalization makes it possible to compare people of different sizes without entering height and weight.
I don't have cystatin C — will the calculation be accurate?
Yes, the basic creatinine-based estimate (CKD-EPI 2021) is a validated screening method. Cystatin C only improves accuracy, especially in borderline cases.
Is an eGFR of 85 a disease?
No. 60–89 (category C2) in a person without signs of kidney damage is usually a normal variant, especially with age. The category is always interpreted together with albuminuria and the trend over time.
What should I do if the result is reduced?
Show the result to your physician. Depending on the category, they will order monitoring over time, further tests (urine albumin/creatinine) and, if needed, refer you to a nephrologist.
