CKD Stages Based on eGFR

Chronic kidney disease is classified into five stages based on eGFR values. This staging system, established by KDIGO (Kidney Disease: Improving Global Outcomes), helps clinicians assess disease severity, plan monitoring frequency, and guide treatment decisions.

Important: eGFR Alone Does Not Confirm CKD

For stages G1 and G2, additional evidence of kidney damage (such as albuminuria with uACR ≥ 30 mg/g, abnormal urine sediment, or imaging abnormalities) must be present for at least 3 months to confirm a CKD diagnosis. An eGFR below 60 sustained for 3 or more months indicates CKD regardless of other markers.

Monitoring Frequency by CKD Stage

KDIGO guidelines recommend monitoring kidney function once per year for stages G1–G2 with low risk, twice per year for stage G3, three times per year for stage G4, and four or more times annually for stage G5. The frequency should increase when albuminuria is elevated or risk of progression is higher.

Albuminuria Categories (ACR)

CKD classification also incorporates albuminuria measured as the urinary albumin-to-creatinine ratio (ACR). Category A1 is normal to mildly increased (under 30 mg/g), A2 is moderately increased (30–300 mg/g), and A3 is severely increased (over 300 mg/g). Higher albuminuria combined with a lower eGFR significantly increases the risk of CKD progression and cardiovascular events.

Understanding eGFR: A Complete Guide

What Is Glomerular Filtration Rate (GFR)?

GFR measures how well your kidneys filter waste products from the blood. It is considered the best overall index of kidney function by major nephrology organisations worldwide. Each kidney contains approximately one million tiny filtering units called nephrons. The glomeruli within these nephrons filter about 180 litres of blood daily, producing roughly 1–2 litres of urine. GFR quantifies this filtering capacity in millilitres per minute, standardised to a body surface area of 1.73 m².

Why Is eGFR Important?

Since directly measuring GFR requires complex procedures involving intravenous tracers, clinicians use estimated GFR (eGFR) calculated from blood test results. eGFR is used to detect kidney disease early, determine CKD stage, adjust medication dosages (since many drugs are cleared by the kidneys), assess cardiovascular risk (reduced kidney function is an independent cardiovascular risk factor), and decide when to refer patients to a nephrologist or initiate dialysis. Normal eGFR varies by age, generally declining naturally from approximately 120 mL/min/1.73m² in young adults to around 70–80 mL/min/1.73m² by age 70.

What Is Serum Creatinine?

Creatinine is a waste product generated from normal muscle metabolism. Your muscles break down a compound called creatine phosphate to produce energy, and creatinine is the byproduct. It is produced at a relatively constant rate and is freely filtered by the kidneys, making it a practical marker for kidney function. Normal serum creatinine ranges are approximately 0.7–1.3 mg/dL for adult males and 0.6–1.1 mg/dL for adult females. However, creatinine levels can be influenced by muscle mass, diet (particularly high protein intake), hydration status, and certain medications.

What Is Cystatin C?

Cystatin C is a small protein produced by all nucleated cells in the body at a relatively constant rate. Unlike creatinine, it is not significantly affected by muscle mass, diet, or sex, making it a complementary biomarker for estimating GFR. The NKF-ASN Task Force recommends using cystatin C to confirm eGFR estimates from creatinine alone, particularly when clinical decision-making depends on precise GFR assessment. Using both biomarkers together provides the most accurate eGFR estimate.

Equations Used in This Calculator

CKD-EPI Creatinine Equation (2021) — This is the current recommended standard endorsed by the NKF and ASN for GFR reporting in the United States and many countries globally. Published by Inker et al. in the New England Journal of Medicine in 2021, this equation was developed to eliminate the use of race as a variable. It uses serum creatinine, age, and sex, and was validated in a diverse population of over 8,000 participants.

CKD-EPI Creatinine–Cystatin C Equation (2021) — Also published by the same group in 2021, this equation incorporates both creatinine and cystatin C, providing superior accuracy. It is the preferred equation when both biomarkers are available and is especially useful when creatinine alone may be misleading (for example, in patients with unusual muscle mass, extremes of body size, or vegetarian diets).

CKD-EPI Cystatin C Equation (2012) — This equation uses only cystatin C and is useful when creatinine measurements may be unreliable. It is unaffected by muscle mass and dietary protein intake.

MDRD Study Equation — The Modification of Diet in Renal Disease equation was developed in 2006 from the Levey et al. study using standardised creatinine. While once widely used, it has been superseded by the CKD-EPI equations, which are more accurate at higher GFR levels. It is included here as a reference.

Limitations of eGFR

eGFR is an estimate and may not precisely reflect actual kidney function in certain populations: individuals with extreme muscle mass (very muscular or very thin/amputee), those following unusual diets (very high protein or strict vegetarian), patients taking medications that affect creatinine secretion, pregnant women, people with acute kidney injury (where creatinine has not yet stabilised), and children under 18 (who require paediatric equations). Trends in eGFR over time are often more informative than a single measurement.

Race and eGFR: The 2021 Update

Prior versions of the CKD-EPI and MDRD equations included a coefficient for Black race, which estimated higher eGFR for the same creatinine values. The 2021 NKF-ASN Task Force concluded that race is a social, not biological, construct and should not be used in eGFR calculations. The 2021 race-free equations have been adopted as the standard. For individuals previously categorised as Black, eGFR using the 2021 equations will generally be lower than the older race-adjusted values. Conversely, for those categorised as non-Black, eGFR may be slightly higher.

Treatment Options for Chronic Kidney Disease

Treatment for CKD depends on its stage and underlying cause. The earlier kidney disease is detected, the more effectively its progression can be slowed. Below is an overview of all available treatment approaches — from everyday lifestyle adjustments to advanced therapies.

When to See a Nephrologist

Referral to a nephrologist is generally recommended when eGFR drops below 30 mL/min/1.73m² (CKD stage G4–G5), when there is persistent albuminuria above 300 mg/g, when eGFR is declining rapidly (more than 5 mL/min/1.73m² per year), when the cause of kidney disease is unclear, or when kidney disease is accompanied by resistant hypertension, electrolyte abnormalities, or recurrent kidney stones. Earlier referral may be appropriate depending on individual circumstances.

Frequently Asked Questions About eGFR