eGFR (estimated glomerular filtration rate) is the single most important number for measuring kidney health. It estimates how many millilitres of blood your kidneys can filter per minute and directly determines your CKD stage. An eGFR of 90 or above with no damage markers is considered normal; an eGFR below 60 for more than three months meets the KDIGO 2024 definition of Chronic Kidney Disease.
The glomerular filtration rate (GFR) is the volume of plasma filtered by the kidneys per unit time. The "e" in eGFR stands for "estimated" — your kidneys are not directly measured but rather estimated from a blood test for serum creatinine, a waste product that healthy kidneys filter out. When kidneys are damaged, creatinine accumulates in the blood, and eGFR falls.
GFR has been used as the primary measure of kidney function since the 1950s. Today, the CKD-EPI 2021 equation is the international standard — endorsed by KDIGO, NKF (National Kidney Foundation), and ASN (American Society of Nephrology). Crucially, the 2021 version removed a race-based correction factor present in the older 2009 formula, eliminating a source of health disparity.
Your doctor sends a blood sample to a laboratory. The lab measures serum creatinine (Scr) in mg/dL and then applies the following formula — or your eGFR is calculated automatically with your age and sex:
You never need to calculate this yourself — your lab report includes eGFR automatically. However, understanding what variables influence it matters:
The 2009 CKD-EPI formula included a race coefficient that added approximately 16% to eGFR for patients identified as Black. This created systemic disparities — Black patients were classified as having better kidney function than they actually had, delaying referrals and transplant listings. The 2021 race-neutral formula was adopted because race is a social construct, not a biological one. All major nephrology bodies now require labs to use the 2021 formula. If your lab report shows both "eGFR (with race)" and "eGFR (without race)", use the race-neutral figure.
| eGFR (mL/min/1.73m²) | CKD Stage | Kidney Function | What to Do |
|---|---|---|---|
| ≥ 90 | G1 | Normal — but investigate if damage markers present | Rule out proteinuria, blood in urine; treat underlying cause |
| 60 – 89 | G2 | Mildly decreased — CKD if damage markers present for >3 months | BP control ≤130/80; RAASi if proteinuric; annual monitoring |
| 45 – 59 | G3a | Mild to moderately decreased | SGLT2i initiation; anaemia screen; bicarbonate monitoring |
| 30 – 44 | G3b | Moderately to severely decreased | Nephrology referral; Metformin dose-halve; potassium restriction |
| 15 – 29 | G4 | Severely decreased | Dialysis preparation; vascular access planning; transplant evaluation |
| < 15 | G5 | Kidney failure | Initiate dialysis or transplant; conservative management if elected |
KDIGO 2024 defines rapid CKD progression as an eGFR decline of more than 5 mL/min/1.73m² per year, OR more than 10% change in eGFR within 12 months. Rapid decliners have significantly increased risk of reaching kidney failure regardless of their current stage. If your eGFR dropped from 60 to 50 in one year, that is a 10-point decline — requiring urgent nephrology review even if your absolute number is still in the "safe" range.
eGFR is not a perfect measure. Several factors can cause temporary fluctuations — important to know before panicking about a single result:
| Marker | What It Measures | Best For | Limitations |
|---|---|---|---|
| eGFR (creatinine-based) | Kidney filtration rate estimated from serum creatinine | Standard CKD staging; routine monitoring | Affected by muscle mass, diet, medications |
| Serum Creatinine | Raw waste product level in blood | Trending over time (directional changes) | Not standardised — varies by lab, sex, muscle mass |
| Cystatin C eGFR | Kidney filtration using cystatin C protein | Elderly, low muscle mass, athletes, obesity | More expensive; affected by thyroid disease, steroids |
| Combined eGFR (Cr+CysC) | Average of creatinine + cystatin C eGFR | Highest accuracy for risk prediction | Requires both tests; not routine |
KDIGO 2024 recommends cystatin C-based or combined eGFR for patients where creatinine-based eGFR may be inaccurate — particularly older adults with low muscle mass, patients with extreme body composition, and those where staging-dependent decisions (transplant listing, drug dosing) require maximum accuracy.
| CKD Stage + Albuminuria | Monitoring Frequency (KDIGO 2024) |
|---|---|
| G1–G2, A1 (<30 mg/g UACR) | Once per year |
| G3a, A1 | Once per year |
| G3a–G3b, A2 (30–300 mg/g) | Every 6 months |
| G3b–G4, A3 (>300 mg/g) | Every 3–4 months |
| G5 | Every 1–3 months |
| After new RAASi/SGLT2i | Within 2–4 weeks |
What is eGFR and what does it measure?
eGFR (estimated glomerular filtration rate) estimates how many mL of blood your kidneys filter per minute per 1.73 m² body surface. It is the primary biomarker for CKD staging, derived from serum creatinine, age, and sex using the CKD-EPI 2021 race-neutral formula endorsed by KDIGO 2024.
What is a normal eGFR level?
An eGFR of 90 or above is normal (G1 stage) without damage markers. eGFR 60–89 is mildly decreased. Below 60 for more than 3 months meets the KDIGO 2024 CKD definition. Note: eGFR naturally declines ~1 mL/min/year with normal aging after age 40.
Can eGFR fluctuate day to day?
Yes — eGFR can vary 10–15% between readings due to hydration, diet (meat intake), exercise, and medications. CKD diagnosis requires eGFR below 60 persisting for more than 3 months, not just a single reading. Always compare trends over multiple measurements.
What is considered a dangerous eGFR level?
eGFR below 30 (Stage G4) is severely decreased and requires urgent nephrology care. eGFR below 15 (Stage G5) is kidney failure. A rapid decline of more than 5 mL/min/year is considered fast CKD progression regardless of absolute eGFR.
How is eGFR affected by muscle mass?
Creatinine is a breakdown product of muscle. Athletes and bodybuilders produce more creatinine naturally, which can make eGFR appear lower than actual kidney function. Conversely, elderly patients and those with low muscle mass may have falsely high eGFR despite reduced kidney function. In these cases, cystatin C-based eGFR is more accurate.