Kidney health
eGFR and Kidney Function: Understanding CKD Stages and CKD-EPI 2021
What does your eGFR number mean? Learn how the CKD-EPI 2021 formula works, the KDIGO 2024 CKD stages (G1–G5), key risk factors for kidney disease, and when to seek medical advice.
Free online tool
eGFR — Kidney function
The estimated Glomerular Filtration Rate (eGFR) is the most widely used measure of kidney function. It estimates how well your kidneys filter waste products from the blood, expressed as millilitres of blood filtered per minute per 1.73 m² of body surface area (mL/min/1.73 m²). A healthy young adult typically has an eGFR above 90. Values below 60 persisting for three or more months indicate chronic kidney disease (CKD).
The CKD-EPI 2021 Formula
The most accurate and currently recommended equation is CKD-EPI 2021 (Inker LA et al., NEJM 2021; PMID 34554658). This updated version removed race as a variable compared to CKD-EPI 2009, reflecting KDIGO 2024 guidance that race-based adjustments introduced systematic bias in clinical care. The formula uses serum creatinine, age, and sex. Optionally, serum cystatin C can be incorporated for greater accuracy in certain populations, such as individuals with low muscle mass or amputees.
Why eGFR is estimated, not measured
True GFR can only be measured directly using inulin clearance or iohexol — expensive, time-consuming procedures reserved for research. eGFR is a validated mathematical approximation from routine blood tests that correlates closely with directly measured GFR and is accurate enough for all clinical decisions in the vast majority of patients.
KDIGO 2024 CKD Staging (G1–G5)
The Kidney Disease: Improving Global Outcomes (KDIGO) 2024 guideline classifies CKD into five GFR categories. Note that CKD diagnosis requires both an eGFR below 60 OR evidence of kidney damage (e.g., albuminuria, structural abnormality) persisting for ≥3 months. A single eGFR reading below 60 is not sufficient for diagnosis.
GFR Categories (KDIGO 2024)
G1 — Normal or high
≥ 90 mL/min/1.73 m²
Normal kidney function. CKD only if other markers of kidney damage are present (e.g., persistent albuminuria, haematuria of renal origin, structural or histological abnormality).
G2 — Mildly decreased
60–89 mL/min/1.73 m²
Mildly reduced filtration. Often normal for older adults. CKD only if other kidney damage markers are present. Monitor annually if risk factors exist.
G3a — Mildly to moderately decreased
45–59 mL/min/1.73 m²
CKD confirmed even without additional damage markers. Increased risk of cardiovascular disease and CKD progression. Nephrology referral advised. Monitor every 6 months.
G3b — Moderately to severely decreased
30–44 mL/min/1.73 m²
Significant reduction. High cardiovascular risk. Nutritional adjustments (protein, phosphate, potassium) may be required. Monitor every 3–6 months.
G4 — Severely decreased
15–29 mL/min/1.73 m²
Severe reduction. Prepare for kidney replacement therapy (dialysis or transplant). Nephrology care is essential. Complication management intensifies.
G5 — Kidney failure
< 15 mL/min/1.73 m²
Kidney failure. Dialysis or kidney transplantation is typically required. Also called end-stage renal disease (ESRD).
Risk Factors for Kidney Disease
Several conditions and lifestyle factors are strongly associated with CKD development and progression. Addressing modifiable risk factors is the most effective way to preserve kidney function over time.
- Diabetes mellitus (types 1 and 2) — the leading cause of CKD worldwide, responsible for approximately 40% of cases.
- Hypertension — elevated blood pressure damages the glomerular filtration membranes over years.
- Cardiovascular disease — heart failure, atherosclerosis, and CKD share bidirectional risk.
- Obesity and metabolic syndrome — associated with hyperfiltration injury and accelerated progression.
- Recurrent urinary tract infections or kidney stones — structural damage accumulates over time.
- Family history of CKD or hereditary nephropathies (e.g., polycystic kidney disease).
- Long-term use of NSAIDs (ibuprofen, naproxen) and certain antibiotics (aminoglycosides).
- Age over 60 — eGFR naturally declines with age; roughly 1 mL/min/1.73 m² per year after age 40.
- Smoking — reduces renal blood flow and accelerates decline in diabetic nephropathy.
- Low birth weight — associated with reduced nephron endowment and higher lifetime CKD risk.
Albuminuria: the Other Half of CKD Assessment
KDIGO 2024 requires assessing both GFR category and albuminuria category (A1–A3) to fully characterise CKD severity and guide treatment decisions. Albuminuria is measured as the urine albumin-to-creatinine ratio (uACR) on a spot urine sample.
Albuminuria Categories (KDIGO 2024)
A1 — Normal to mildly increased
< 30 mg/g (< 3 mg/mmol)
Normal range in most adults. In diabetic patients, levels 10–30 mg/g may indicate early diabetic nephropathy (formerly 'microalbuminuria').
A2 — Moderately increased
30–300 mg/g (3–30 mg/mmol)
Significantly elevated. Strong independent predictor of CKD progression and cardiovascular events. ACE inhibitor or ARB therapy is typically initiated.
A3 — Severely increased
> 300 mg/g (> 30 mg/mmol)
Nephrotic-range proteinuria if >2000 mg/g. Rapid progression risk. Nephrology referral mandatory.
How to Protect Your Kidneys
While some causes of CKD are not preventable, evidence-based lifestyle measures can significantly slow progression or prevent disease in at-risk individuals.
- Control blood pressure to <130/80 mmHg (KDIGO 2024 target for most CKD patients).
- Manage blood glucose meticulously if diabetic; target HbA1c <7% unless individualized.
- Avoid prolonged or high-dose NSAID use; use paracetamol (acetaminophen) instead for pain.
- Stay well hydrated — aim for pale yellow urine as a practical guide.
- Follow a kidney-appropriate diet: limit sodium (<2 g/day), moderate protein intake, restrict phosphate and potassium in advanced CKD.
- Quit smoking — it independently accelerates CKD progression.
- Maintain a healthy BMI; weight loss in obese patients reduces proteinuria.
- Get regular eGFR and uACR monitoring if you have diabetes, hypertension, or family history of CKD.
When to See a Doctor
A single low eGFR reading may be transient (due to dehydration, recent intense exercise, or acute illness). Repeat testing after 2–4 weeks before drawing conclusions. Seek prompt medical evaluation for any of the following:
- eGFR below 60 on two separate occasions ≥3 months apart.
- Rapid decline of >5 mL/min/1.73 m² over 12 months.
- Urine that is persistently foamy (suggesting proteinuria) or blood-tinged.
- Swelling of ankles, feet, or face not explained by other causes.
- Persistent fatigue, nausea, or difficulty concentrating without clear cause.
- Any eGFR below 30 — nephrology referral is recommended regardless of trajectory.
Sources
- Inker LA et al. New Creatinine– and Cystatin C–Based Equations to Estimate GFR without Race. N Engl J Med. 2021;385(19):1737–1749. PMID 34554658.
- KDIGO 2024 CKD Guideline. Kidney International. 2024;105(4S):S117–S314.
- Levey AS, Coresh J. Chronic kidney disease. Lancet. 2012;379(9811):165–180. PMID 21840587.
- Stevens PE, Levin A; Kidney Disease: Improving Global Outcomes CKD Guideline Development Work Group Members. Evaluation and management of chronic kidney disease: synopsis of the kidney disease: improving global outcomes 2012 clinical practice guideline. Ann Intern Med. 2013;158(11):825–830. PMID 23732715.
