What is eGFR?
eGFR (estimated glomerular filtration rate) is a calculated measure of kidney function that estimates how much blood the kidneys filter per minute, reported in mL/min/1.73 m², and serves as the primary clinical tool for diagnosing and staging chronic kidney disease. 1
Definition and Clinical Significance
eGFR represents an estimate of the glomerular filtration rate—the best available index of overall kidney function 2. Normal GFR values are approximately 130 mL/min/1.73 m² for men and 120 mL/min/1.73 m² for women 3.
The key threshold to remember: eGFR <60 mL/min/1.73 m² indicates chronic kidney disease (CKD) when persistent 4, 5. This cutoff is clinically validated, as measured GFR values of 60 mL/min/1.73 m² are associated with significantly higher rates of mortality and kidney failure compared to 90 mL/min/1.73 m² 6.
How eGFR is Calculated
eGFR is derived from mathematical equations using:
- Serum creatinine (most common)
- Age
- Sex
- Optionally: cystatin C for improved accuracy 7
The most widely used equations are:
- CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration): Most accurate, especially at GFR >60 mL/min/1.73 m², and better predictor of adverse outcomes 3
- MDRD (Modification of Diet in Renal Disease): Performs better at GFR <60 mL/min/1.73 m² but underestimates at higher values 3
Important update: Current guidelines recommend race-free eGFR equations 8, 9. The 2024 KDIGO guidelines endorse body surface area-adjusted eGFR without race correction 7, 9.
Clinical Staging Using eGFR
The GFR categories define CKD stages 1, 5:
- G1: ≥90 mL/min/1.73 m² (normal/increased, but kidney damage present)
- G2: 60-89 mL/min/1.73 m² (mildly reduced)
- G3a: 45-59 mL/min/1.73 m² (moderately reduced)
- G3b: 30-44 mL/min/1.73 m² (moderately to severely reduced)
- G4: 15-29 mL/min/1.73 m² (severely reduced)
- G5: <15 mL/min/1.73 m² (kidney failure)
When eGFR May Be Inaccurate
Use eGFR with caution or consider confirmatory testing in 3, 7:
- Extremes of muscle mass (bodybuilders, amputees, severe malnutrition)
- Extremes of body weight (obesity, cachexia)
- Rapidly changing kidney function (acute kidney injury)
- Pregnancy
- Certain medications affecting creatinine secretion
In these situations, consider measuring cystatin C and using eGFRcr-cys (combined creatinine-cystatin C equation) for better accuracy 7. When precision is critical for major clinical decisions, measured GFR using exogenous filtration markers (iohexol, iothalamate) provides the gold standard 2, 7.
Practical Clinical Applications
eGFR guides critical decisions 8:
- Drug dosing: Many medications require adjustment based on eGFR thresholds
- CKD diagnosis and staging: Combined with albuminuria for complete assessment 1
- Nephrology referral: Consider referral at eGFR <45 mL/min/1.73 m² or with progressive decline 3
- Treatment eligibility: SGLT2 inhibitors, ACE inhibitors, and other therapies have eGFR-based prescribing criteria 8
Key monitoring recommendation: Check eGFR at least annually in all adults with diabetes, and at diagnosis plus annually in those with hypertension or CKD risk factors 4, 5.
The combination of eGFR with urine albumin-creatinine ratio (UACR) provides the most complete assessment of kidney health and risk stratification 1, 5.