The glomerular filtration rate (GFR) is the most important marker for assessing kidney function. It measures how much blood your kidneys filter per minute. A low value indicates impaired kidney function.
Because directly measuring GFR is complex, clinical practice uses the estimated GFR (eGFR), calculated from serum creatinine, age, and sex. The CKD-EPI 2021 equation is the current gold standard.
What Is Glomerular Filtration Rate?
The glomeruli are tiny filtering units in the kidneys — about one million per kidney. Together they filter roughly 180 liters of blood per day, corresponding to an eGFR of 90–120 mL/min/1.73 m² in healthy adults.
eGFR is normalized to a standard body surface area of 1.73 m² to allow comparison between people of different sizes. Values above 60 are generally sufficient for everyday life; below that, chronic kidney disease (CKD) is indicated.
The CKD-EPI 2021 Equation
CKD-EPI 2021 (Chronic Kidney Disease Epidemiology Collaboration) is the equation recommended by KDIGO (Kidney Disease: Improving Global Outcomes). It replaced the older CKD-EPI 2009, which included a race-based correction factor that has since been removed for equity and accuracy reasons.
Compared to the older MDRD formula, CKD-EPI is more accurate in the normal and mildly elevated range — precisely where early kidney damage needs to be detected.
CKD Stages (KDIGO)
KDIGO classifies chronic kidney disease into six stages:
| Stage | eGFR (mL/min/1.73m²) | Description |
|---|---|---|
| G1 | ≥ 90 | Normal or high |
| G2 | 60 – 89 | Mildly decreased |
| G3a | 45 – 59 | Mildly to moderately decreased |
| G3b | 30 – 44 | Moderately to severely decreased |
| G4 | 15 – 29 | Severely decreased |
| G5 | < 15 | Kidney failure |
Important: A single eGFR value is not a diagnostic criterion. CKD is only diagnosed when abnormalities persist for at least 3 months.
Serum Creatinine: mg/dL and µmol/L
Creatinine is a metabolic byproduct of muscle activity. It is almost exclusively eliminated by the kidneys, making elevated creatinine a marker of reduced filtration.
Creatinine is reported in mg/dL in the US and some countries, and in µmol/L elsewhere. The conversion:
Normal values: men 0.7–1.2 mg/dL (62–106 µmol/L), women 0.5–1.0 mg/dL (44–88 µmol/L). Older adults and people with low muscle mass tend to have lower values.
When to See a Doctor
Inform your primary care doctor and have risk factors (blood pressure, blood sugar) monitored regularly.
Regular follow-up visits with your primary care doctor or nephrologist (at least once a year).
See a nephrologist. Close monitoring and medication adjustments are required.
Urgent nephrology referral. Discuss preparation for dialysis or kidney transplantation.
Related Health Calculators
Kidney function is closely linked to other health parameters. These calculators help with a comprehensive assessment:
- Blood Pressure Calculator — Hypertension is one of the most common causes of kidney disease.
- Blood Sugar Converter — Diabetes is the second most common cause of CKD.
- BMI Calculator — Obesity increases the risk of kidney and cardiovascular disease.