GFR Calculator
The CKD-EPI 2021 equation calculates eGFR from serum creatinine, age, and sex. Creatinine is a waste product filtered by...
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How It Works
The CKD-EPI 2021 equation calculates eGFR from serum creatinine, age, and sex. Creatinine is a waste product filtered by the kidneys. Higher creatinine = lower GFR = reduced kidney function. The equation uses different constants for males and females to account for typical differences in muscle mass.
Quick Reference
GFR ≥ 90
Normal or high
Stage 1 (Normal)
GFR 60-89
Mildly decreased
Stage 2
GFR 30-59
Moderately decreased
Stage 3
GFR < 15
Kidney failure
Stage 5
Tips & Shortcuts
eGFR naturally declines about 1 mL/min/1.73m² per year after age 40 — this is normal aging.
A single low reading may be due to dehydration, recent intense exercise, or muscle injury. Repeat testing confirms chronic kidney disease.
Creatinine-based eGFR may overestimate kidney function in people with very low muscle mass (elderly, malnourished). Cystatin C is a more accurate alternative.
Common Mistakes
Diagnosing kidney disease from one test
CKD requires at least 2 eGFR readings below 60 mL/min/1.73m², at least 3 months apart.
Ignoring eGFR decline even if still above 60
A consistent drop of 5+ mL/min/1.73m² per year is clinically significant even in the "normal" range. Track trends, not single values.
Frequently Asked Questions
eGFR measures kidney filtering efficiency. Above 90: normal. 60–89: mildly decreased. 30–59: moderately decreased. 15–29: severely decreased. Below 15: kidney failure.
The 2021 update removed the race adjustment after research showed it had no strong physiological basis and led to underestimating kidney disease severity in Black patients.
Common causes: diabetes (leading cause), hypertension, glomerulonephritis, polycystic kidney disease. GFR naturally declines about 1 mL/min/year after age 40.
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