A complete guide to estimated GFR — how it's calculated using CKD-EPI 2021, how to stage CKD, what each stage means clinically, and how eGFR differs from creatinine clearance.
Your kidneys filter around 180 litres of blood every day — nearly 125 mL every minute. They remove waste products, regulate blood pressure, control fluid balance, produce hormones that stimulate red blood cell production, and activate vitamin D for bone health. When the kidneys start failing, none of these functions can be substituted by any other organ.
Chronic kidney disease (CKD) affects approximately 850 million people worldwide — making it more common than diabetes. In India, an estimated 17% of the urban adult population has some form of CKD. Most of them don't know it — because CKD is largely silent until it is advanced.
The estimated Glomerular Filtration Rate (eGFR) is the single most important number in kidney medicine. It tells you how well the kidneys are filtering, stages the severity of kidney disease, guides treatment decisions, determines when to refer to a nephrologist, and predicts the risk of kidney failure. Understanding eGFR is essential for anyone with kidney disease — and for every clinician who manages patients with diabetes, hypertension, or cardiovascular disease.
The glomerular filtration rate (GFR) is the volume of fluid filtered from the glomerular capillaries into Bowman's capsule per unit time — essentially, how many millilitres of blood the kidneys filter per minute.
True GFR can only be measured by infusing a substance like inulin that is freely filtered and neither secreted nor reabsorbed by the tubules, then measuring its clearance. This is cumbersome, expensive, and impractical for routine clinical use.
Instead, clinicians use serum creatinine — combined with age, sex, and occasionally other factors — to estimate GFR. This is the estimated GFR (eGFR). While not perfect, eGFR is accurate enough for clinical staging of CKD and monitoring of kidney function over time.
The most widely used and currently recommended equation is the CKD-EPI Creatinine Equation (2021 revision), developed by the Chronic Kidney Disease Epidemiology Collaboration.
The formula looks complex, but the key inputs are straightforward: serum creatinine, age, and sex. Most laboratories now automatically report eGFR alongside every serum creatinine result. The formula is also built into calculators, EMRs, and point-of-care tools.
🫘 Use the RxMedCalc eGFR Calculator — supports both CKD-EPI 2021 and MDRD equations, with automatic CKD staging.
The 2009 version of CKD-EPI (and the older MDRD equation before it) included a race coefficient that assigned higher eGFR values to Black patients. This was based on the observation that Black individuals had, on average, higher serum creatinine values for the same measured GFR — possibly reflecting higher average muscle mass.
The 2021 revision removed this race adjustment for several important reasons:
The CKD-EPI 2021 race-free equation is now recommended by KDIGO, ASN, and most major nephrology societies worldwide.
Kidney disease is staged using both eGFR (G categories) and albuminuria (A categories). eGFR alone captures the degree of filtration loss; albuminuria captures kidney damage even before filtration is significantly impaired.
| Stage | eGFR (mL/min/1.73m²) | Description | Key Clinical Actions |
|---|---|---|---|
| G1 | ≥ 90 | Normal or high — but kidney damage present (e.g. proteinuria) | Treat underlying cause; control BP and blood sugar |
| G2 | 60–89 | Mildly reduced kidney function | Monitor annually; cardiovascular risk reduction |
| G3a | 45–59 | Mild-to-moderate reduction | Monitor every 6 months; review all medications for renal dosing |
| G3b | 30–44 | Moderate-to-severe reduction | Nephrology referral; phosphate monitoring; anaemia assessment |
| G4 | 15–29 | Severely reduced | Prepare for renal replacement therapy; dietitian referral |
| G5 | < 15 | Kidney failure | Dialysis or transplant; or conservative management if chosen |
⚠️ CKD requires two readings > 3 months apart. A single low eGFR does not diagnose CKD — it could represent acute kidney injury (AKI). CKD is only diagnosed when kidney function is reduced or kidney damage (proteinuria, haematuria, structural abnormality) is present for more than 3 months.
Albuminuria (protein in the urine) is a key marker of kidney damage. It is measured as the urine albumin-to-creatinine ratio (uACR) on a spot urine sample:
A patient can have G1 eGFR (normal filtration) but A3 albuminuria — this still constitutes CKD, because proteinuria itself indicates kidney damage even when GFR is preserved. This is common in early diabetic nephropathy. Together, the G and A categories create a risk grid (KDIGO heat map) that guides monitoring frequency and intensity of treatment.
The two leading causes of CKD worldwide — and in India — are diabetes mellitus and hypertension. Together they account for over 60% of all CKD cases.
| Cause | Mechanism | Key Feature |
|---|---|---|
| Diabetic nephropathy | Glomerular hyperfiltration → glomerulosclerosis | Early microalbuminuria; progresses over years |
| Hypertensive nephrosclerosis | Arteriolar sclerosis → ischaemic glomerular injury | Gradual decline in eGFR; mild proteinuria |
| Glomerulonephritis | Immune-mediated glomerular inflammation | Haematuria + proteinuria; often younger patients |
| Polycystic kidney disease (ADPKD) | Progressive cyst formation destroying parenchyma | Family history; large kidneys on ultrasound |
| Obstructive uropathy | Chronic obstruction → back-pressure injury | Prostatic disease, stones, congenital abnormalities |
| Recurrent UTIs / pyelonephritis | Repeated infection → scarring | Common in women; often underdiagnosed |
| Drug-induced nephropathy | Direct tubular toxicity or interstitial nephritis | NSAIDs, aminoglycosides, contrast agents, lithium |
CKD is notoriously asymptomatic until it is advanced. Most patients with G1–G3 CKD have no symptoms at all. This is why screening high-risk groups (diabetics, hypertensives, those with family history of kidney disease) is essential.
Symptoms typically begin to appear at G4 and G5, and include:
CKD is often progressive, but the rate of progression varies enormously. With optimal management, many patients — particularly those with early CKD — never reach kidney failure in their lifetime.
Target BP in CKD is generally < 120/80 mmHg (KDIGO 2024 update), or < 130/80 if proteinuria is present. ACE inhibitors (e.g. ramipril, enalapril) or ARBs (e.g. losartan, telmisartan) are the preferred antihypertensive agents in CKD — they reduce intraglomerular pressure and slow proteinuria-driven damage. Do not combine an ACEi and ARB (dual blockade) — this increases harm without additional benefit.
Target HbA1c ~7% (53 mmol/mol) in most patients with diabetic CKD. SGLT2 inhibitors (empagliflozin, dapagliflozin, canagliflozin) are now first-line in diabetic CKD alongside metformin — they reduce intraglomerular hyperfiltration and have demonstrated significant reductions in CKD progression and cardiovascular events in large clinical trials. Check eGFR before prescribing: most SGLT2 inhibitors require eGFR ≥ 20–25 for initiation.
Finerenone (a novel non-steroidal mineralocorticoid receptor antagonist) is also approved for CKD in type 2 diabetes, with evidence for reducing CKD progression and cardiovascular events.
KDIGO guidelines recommend nephrology referral when:
📌 eGFR (CKD-EPI) is used for diagnosing and staging CKD. Creatinine clearance (Cockcroft-Gault) is used for adjusting drug doses. They serve different purposes and should not be used interchangeably. See our companion article: Creatinine Clearance & the Cockcroft-Gault Equation →
Patient: 58-year-old woman with a 10-year history of type 2 diabetes and hypertension. Routine blood test shows serum creatinine 1.6 mg/dL. Spot urine shows uACR 380 mg/g.
eGFR (CKD-EPI 2021): ~38 mL/min/1.73 m² (using age 58, female, SCr 1.6 mg/dL)
CKD Stage: G3b (eGFR 30–44) + A3 (uACR > 300) = very high risk on KDIGO heat map
This patient requires: ACEi or ARB for BP and proteinuria, SGLT2 inhibitor (check eGFR eligibility), dietitian review, phosphate and potassium monitoring, anaemia workup, review of all medications for renal dosing, and nephrology referral given eGFR < 45 with severe proteinuria. Stop NSAIDs if being used.
🫘 Calculate your eGFR and see your CKD stage instantly: RxMedCalc eGFR Calculator →
This article is written for educational purposes based on KDIGO and CKD-EPI guidelines current at time of publication. It is not a substitute for professional medical advice. CKD management should always be individualised and guided by a qualified physician or nephrologist.
Built by an MBBS, AFIH Certified Physician in Punjab, India | RxMedCalc.com