Estimated Glomerular Filtration Rate (eGFR)
eGFR is the gold standard for kidney function assessment — it estimates how much blood your kidneys filter per minute. Calculated from creatinine (and/or cystatin C) using equations that adjust for age and sex. eGFR is used to diagnose CKD, determine its stage (1-5), guide medication dosing, and decide on dialysis/transplant timing. Below 60 for 3+ months = CKD; below 15 = kidney failure.
The estimated glomerular filtration rate (eGFR) is the best overall measure of kidney function. It estimates how much blood your kidneys filter per minute — specifically, how well the glomeruli (the kidney’s filtering units) are working. Rather than measuring filtration directly, eGFR is calculated from creatinine (and sometimes cystatin C) using equations that account for age and sex.
Why does this matter? eGFR is the foundation of kidney disease diagnosis and management. It’s used to detect chronic kidney disease (CKD), determine its stage, guide medication dosing, decide when to refer to nephrology, and determine eligibility for kidney transplant or dialysis. A single number tells you — and your healthcare team — how well your kidneys are functioning.
eGFR has largely replaced creatinine alone for kidney assessment because it provides a more accurate and standardized measure. Labs automatically calculate and report eGFR whenever creatinine is measured.
Key Benefits of Testing
eGFR provides a single, standardized number representing kidney function that’s comparable across patients and over time. This makes it easier to track kidney health, communicate between healthcare providers, and apply clinical guidelines consistently.
This calculated value also adjusts for factors affecting creatinine (age, sex) that could otherwise mislead interpretation. An elderly woman and a young man with the same creatinine have very different kidney function — eGFR captures this difference.
What Does This Test Measure?
eGFR estimates the glomerular filtration rate — the volume of blood filtered by the kidney glomeruli per minute. It’s expressed as milliliters per minute per 1.73 square meters of body surface area, allowing comparison across different body sizes.
How eGFR Is Calculated
eGFR is not directly measured — it’s calculated from blood tests using validated equations:
From creatinine alone: The most common method. Equations like CKD-EPI use creatinine plus age and sex to estimate GFR.
From cystatin C alone: An alternative when creatinine may be unreliable (unusual muscle mass). Uses cystatin C plus age and sex.
From both creatinine and cystatin C: The most accurate approach. Combined equations use both markers for the best estimate.
What the Glomeruli Do
Each kidney contains about one million glomeruli — tiny filtering units that clean your blood. They filter waste products (like creatinine and urea) while retaining blood cells and proteins. The total filtering capacity of all glomeruli is the GFR.
As kidney disease progresses, glomeruli are damaged or destroyed, reducing total filtering capacity. eGFR quantifies this decline.
Why “Estimated”?
True GFR can only be measured directly using complex procedures (like inulin clearance) not practical for routine care. eGFR equations estimate true GFR from simpler blood tests with reasonable accuracy for clinical decisions.
Why This Test Matters
Diagnoses Chronic Kidney Disease
CKD is defined by eGFR below 60 persisting for at least three months, or by markers of kidney damage (proteinuria, abnormal imaging) regardless of eGFR. eGFR is the primary diagnostic criterion.
Stages Chronic Kidney Disease
eGFR determines CKD stage, which guides management intensity and prognosis:
Stage 1: eGFR 90 or above with kidney damage markers — normal filtration but damage present
Stage 2: eGFR 60-89 with kidney damage markers — mildly decreased
Stage 3a: eGFR 45-59 — mild to moderately decreased
Stage 3b: eGFR 30-44 — moderately to severely decreased
Stage 4: eGFR 15-29 — severely decreased
Stage 5: eGFR below 15 — kidney failure (may need dialysis or transplant)
Guides Medication Dosing
Many medications are eliminated by the kidneys or can harm them. eGFR determines:
- Whether certain drugs are safe to use
- Appropriate doses for kidney-cleared medications
- Need for monitoring during treatment
- Contraindications for specific drugs
Predicts Prognosis
Lower eGFR correlates with increased risk of kidney failure, cardiovascular events, and death. Combined with albuminuria, eGFR helps predict outcomes and guide treatment intensity.
Determines Referral Timing
Guidelines recommend nephrology referral at specific eGFR thresholds to ensure specialized care as kidney disease advances.
Guides Dialysis and Transplant Planning
eGFR helps determine when to prepare for renal replacement therapy and eligibility for transplant evaluation.
What Can Affect Your eGFR?
Factors Affecting Kidney Function (True eGFR Changes)
Conditions that lower eGFR:
- Chronic kidney disease from any cause
- Acute kidney injury
- Diabetes — leading cause of CKD worldwide
- Hypertension — second leading cause
- Glomerulonephritis and other primary kidney diseases
- Polycystic kidney disease
- Urinary obstruction
- Nephrotoxic medications
- Aging — GFR naturally declines with age
Factors that may improve eGFR:
- Treatment of reversible causes (obstruction, dehydration)
- Blood pressure control
- Diabetes management
- Discontinuing nephrotoxic drugs
- Recovery from acute kidney injury
Factors Affecting eGFR Accuracy (Not True Kidney Changes)
Creatinine-based eGFR limitations:
- Very high muscle mass — overestimates creatinine, underestimates eGFR
- Very low muscle mass — underestimates creatinine, overestimates eGFR
- Amputees, muscle wasting conditions
- High protein diet or creatine supplements
- Recent intense exercise
- Certain medications affecting creatinine secretion
When to consider cystatin C-based eGFR:
- Borderline creatinine-based eGFR (near 60)
- Unusual muscle mass
- Discrepancy between creatinine and clinical picture
Testing Considerations
eGFR is calculated from creatinine (and/or cystatin C) measured in a blood sample. No fasting required for creatinine. Avoid intense exercise before testing. A single eGFR can be affected by acute changes — trends over time are more reliable than single values.
When Should You Get Tested?
Risk Factors for Kidney Disease
Regular eGFR monitoring is recommended for:
- Diabetes — at least annually
- Hypertension — at least annually
- Cardiovascular disease
- Family history of kidney disease
- Age over 60
- Obesity
- Certain ethnic backgrounds with higher CKD risk
Known Kidney Disease
Frequency depends on CKD stage:
- Stage 1-2: At least annually
- Stage 3a: Every 6-12 months
- Stage 3b: Every 3-6 months
- Stage 4: Every 3 months
- Stage 5: Monthly or as directed by nephrologist
Before Starting Certain Medications
Baseline eGFR is needed before medications that require kidney function assessment — metformin, contrast dye, certain antibiotics, ACE inhibitors, and many others.
Symptoms of Kidney Problems
Changes in urination, swelling, fatigue, or other symptoms suggesting kidney issues warrant eGFR testing.
Routine Health Screening
eGFR is automatically calculated when creatinine is measured as part of basic or comprehensive metabolic panels.
Understanding Your Results
eGFR is reported as a number representing kidney filtration. Labs provide reference information and often indicate CKD stage:
90 or above: Normal kidney function (if no kidney damage markers). Some labs report “>90” or “>60” rather than exact values at higher levels.
60-89: Mildly decreased. May be normal for age in older adults. Only indicates CKD if kidney damage markers (proteinuria, abnormal imaging) are present.
45-59 (Stage 3a): Mild to moderate decrease. CKD is present. Increased cardiovascular risk. Closer monitoring needed.
30-44 (Stage 3b): Moderate to severe decrease. Significant CKD. Higher complication risk. May need nephrology involvement.
15-29 (Stage 4): Severely decreased. Advanced CKD. Nephrology care essential. Prepare for possible dialysis/transplant.
Below 15 (Stage 5): Kidney failure. Dialysis or transplant typically needed to sustain life.
Combining eGFR with Albuminuria
Kidney disease prognosis depends on both eGFR and albuminuria (protein in urine). Someone with eGFR of 50 and significant albuminuria has worse prognosis than someone with eGFR of 50 and no albuminuria. Both should be assessed together.
Trends Matter More Than Single Values
A single eGFR can fluctuate with hydration, illness, or lab variation. Trends over months to years provide more reliable assessment. Rapid decline warrants urgent evaluation; stable values are reassuring.
What to Do About Abnormal Results
For Mildly Reduced eGFR (60-89)
Confirm with repeat testing: Single values can be misleading. Repeat in 3 months to confirm persistence.
Check for kidney damage markers: Urinalysis, urine albumin/creatinine ratio. Without damage markers, this may be normal variation.
Optimize risk factors:
- Control blood pressure
- Manage diabetes if present
- Maintain healthy weight
- Avoid nephrotoxic medications
For Moderately Reduced eGFR (30-59)
Establish CKD diagnosis: If persistent for 3+ months, CKD is confirmed.
Identify and treat underlying cause:
- Optimize diabetes and blood pressure control
- Consider ACE inhibitor or ARB if proteinuria present
- Evaluate for reversible causes
Manage CKD complications:
- Monitor and manage anemia, bone disease, electrolytes
- Avoid nephrotoxic drugs and adjust medication doses
- Cardiovascular risk reduction
Consider nephrology referral: Especially for eGFR below 45, rapid decline, or uncertain diagnosis.
For Severely Reduced eGFR (Below 30)
Nephrology care essential: Specialized management needed.
Prepare for renal replacement: Discuss dialysis options and transplant evaluation if appropriate.
Intensive management: Careful medication dosing, diet modification, complication prevention.
Related Health Conditions
Chronic Kidney Disease
Defined by eGFR: CKD is diagnosed and staged primarily by eGFR. The lower the eGFR, the more advanced the disease. Progression can often be slowed with treatment.
Diabetic Kidney Disease
Leading Cause of CKD: Diabetes damages kidney glomeruli over time, progressively lowering eGFR. Good glucose and blood pressure control slows progression.
Hypertensive Nephropathy
Second Leading Cause: Uncontrolled high blood pressure damages kidney blood vessels. Blood pressure control is essential for preserving eGFR.
Acute Kidney Injury
Sudden eGFR Drop: Rapid decline in eGFR over hours to days from dehydration, medications, obstruction, or acute illness. Often reversible with treatment.
Glomerulonephritis
Inflammatory Kidney Disease: Various conditions causing glomerular inflammation and damage, reducing eGFR. May require specific immunologic treatment.
Why Regular Testing Matters
Kidney disease is often silent until advanced. Regular eGFR monitoring catches decline early — when interventions are most effective. For those with diabetes, hypertension, or other risk factors, annual testing can detect CKD before symptoms develop.
Tracking eGFR trends over time reveals whether kidney function is stable, slowly declining, or rapidly worsening — each requiring different management approaches.
Related Biomarkers Often Tested Together
Creatinine — Used to calculate eGFR. Measured in the same blood sample.
Cystatin C — Alternative or addition to creatinine for more accurate eGFR in certain populations.
BUN — Another kidney marker. BUN/creatinine ratio provides additional diagnostic information.
Urine Albumin/Creatinine Ratio (UACR) — Detects kidney damage (proteinuria). Combined with eGFR for complete kidney assessment.
Potassium — Often elevated in advanced CKD. Requires monitoring.
Phosphate — Rises with declining eGFR. Important for CKD bone disease management.
Note: Information provided in this article is for educational purposes and doesn’t replace personalized medical advice.
Frequently Asked Questions
eGFR (estimated glomerular filtration rate) is a calculated measure of how well your kidneys filter blood. It estimates how much blood your kidney glomeruli filter per minute and is the primary measure used to diagnose and stage chronic kidney disease.
eGFR is calculated from creatinine (and/or cystatin C) using equations that also factor in age and sex. Labs automatically calculate and report eGFR whenever creatinine is measured.
Normal eGFR is generally 90 or above. Values of 60-89 may be normal, especially in older adults, unless kidney damage markers are present. Below 60 for three or more months indicates chronic kidney disease.
Low eGFR indicates reduced kidney filtering ability. The lower the number, the less kidney function remains. Below 60 suggests chronic kidney disease; below 15 indicates kidney failure potentially requiring dialysis or transplant.
Sometimes. If the cause is reversible (dehydration, obstruction, medication), eGFR can improve with treatment. In chronic kidney disease, treatment aims to slow decline rather than restore function, though stabilization is possible with good management.
Creatinine varies with muscle mass, age, and sex. An elderly woman and young man with the same creatinine have very different kidney function. eGFR equations adjust for these factors, providing a standardized, more accurate assessment.
No fasting required. eGFR is calculated from creatinine, which isn’t significantly affected by recent meals. Avoid intense exercise before testing.
For those with risk factors (diabetes, hypertension): at least annually. For established CKD: every 3-12 months depending on stage. For acute concerns: more frequently until stable.
References
Key Sources:
- KDIGO 2012 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int Suppl. 2013;3(1):1-150.
- Inker LA, et al. New creatinine- and cystatin C-based equations to estimate GFR. N Engl J Med. 2021;385(19):1737-1749.
- Levey AS, et al. A new equation to estimate glomerular filtration rate. Ann Intern Med. 2009;150(9):604-612.
