GFR is the volume of blood the kidneys clean per minute. It is the main measure of their work: it is what defines the stage of chronic kidney disease.
GFR is hard to measure directly, so in practice eGFR (estimated) is calculated with the CKD-EPI formula — from creatinine, age and sex. This estimate is more accurate than bare creatinine because it accounts for age and muscle mass.
Reference ranges
Chronic kidney disease stages by eGFR (mL/min/1.73 m²):
| G1 — normal or high | 90 and above |
| G2 — mildly decreased | 60 – 89 |
| G3a — moderately decreased | 45 – 59 |
| G3b — substantially decreased | 30 – 44 |
| G4 — severely decreased | 15 – 29 |
| G5 — kidney failure | below 15 |
What an elevated level means
A high eGFR (above 120) is usually not a problem, but sometimes it reflects hyperfiltration — a state in which the kidneys are working under overload.
This is seen in the early stages of diabetes and in obesity and is considered an unfavorable sign: over time hyperfiltration "wears out" the glomeruli and precedes a decline in function.
What a low level means
A falling eGFR means the kidneys filter the blood less well. A sustained drop below 60 over 3 months is the criterion for chronic kidney disease.
The main causes of CKD: diabetes and arterial hypertension account for the majority of cases. Next come glomerulonephritis, polycystic kidney disease and long-term NSAID use.
The insidious thing about CKD is that it runs silently for years: complaints appear only when 70–80% of function is already lost. That is why eGFR is a screening test, not a "test for symptoms".
How the test is done
eGFR is not tested on its own — it is calculated from blood creatinine. It is enough to test creatinine and ask the lab (or a calculator) to compute eGFR using CKD-EPI.
The conditions are the same as for creatinine: fasting, without strength training or a meat meal the day before, and not dehydrated. To assess kidney damage, eGFR is complemented by a urine test for albumin (albuminuria).
What affects the value
- Age — eGFR naturally declines by about 1 mL/min per year after 40.
- Diabetes and hypertension — the main causes of kidney damage.
- Dehydration — temporarily lowers eGFR.
- NSAIDs — regular use of painkillers damages the kidneys.
- Muscle mass — acts through creatinine and can distort the estimate.
- Contrast agents at CT — can temporarily worsen function.
Calculate using this marker
Calculators where GFR is used directly:
Frequently asked questions
Is an eGFR of 75 bad?
That is stage G2 — "mildly decreased". On its own it is not considered kidney disease if there are no signs of damage (such as albuminuria). But it is a reason to control blood pressure and glucose and to repeat the test in a few months.
Can GFR be restored?
Lost nephrons do not regenerate, but progression can be slowed dramatically: control blood pressure and glucose, stop NSAIDs, cut salt and protein load. The earlier you start, the more function you can preserve.
Why is eGFR more important than creatinine?
Because creatinine depends on muscle mass: in a slim elderly person it can look "normal" even when kidney function is already reduced. eGFR accounts for age and sex and so detects the problem earlier.