eGFR Test: Meaning, Importance, Causes, Symptoms, Normal Range, and Complete Guide
Introduction
The eGFR test, also known as the Estimated Glomerular Filtration Rate, is one of the most important tests to assess kidney health. It helps doctors understand how well your kidneys filter waste, toxins, and excess fluid from the bloodstream. Unlike many blood tests that measure actual substances, eGFR is a calculated value based on the level of creatinine in your blood along with your age, gender, and sometimes race. Because kidney disease often has no early symptoms, the eGFR test plays a critical role in detecting problems before they become severe.
A declining eGFR value signals reduced kidney function. Doctors also use this test to determine the stage of Chronic Kidney Disease (CKD), monitor ongoing kidney conditions, and decide when treatments such as medication, dialysis, or transplantation may be required.
What is eGFR?
eGFR stands for Estimated Glomerular Filtration Rate. It reflects how many milliliters of blood your kidneys filter per minute per 1.73 m² of body surface area. A healthy kidney filters waste continuously, and eGFR provides a numerical estimate of this capacity.
Instead of measuring kidney filtration directly—which is difficult, time-consuming, and expensive—eGFR uses a mathematical formula beside your creatinine level. The result gives an approximate picture of your kidney’s filtering ability.
How is eGFR Calculated?
eGFR is not produced inside the body. Instead, it is calculated using formulas that include:
- Serum Creatinine Level – obtained through a simple blood test
- Age – kidney function naturally decreases with age
- Gender – muscle mass differs between men and women
- Race (used only in older equations, not in the latest recommended models)
The most widely used formulas are:
CKD-EPI Equation
This is the most accurate and is currently the preferred method. It adjusts for age and gender and is more reliable for high and low creatinine values.
MDRD Equation
An older method still used in some laboratories. It may underestimate kidney function in people with normal or near-normal creatinine levels.
These formulas correct for changes in muscle mass, making eGFR far more reliable than creatinine alone.
Main Functions and Importance of eGFR
The eGFR test is essential for evaluating and monitoring kidney health. Its importance includes:
Early Detection of Kidney Damage
Kidney disease often progresses silently. eGFR detects issues long before symptoms appear, allowing early treatment.
Staging Chronic Kidney Disease (CKD)
Based on eGFR, doctors classify CKD into five stages. This helps determine how advanced the condition is and what interventions are needed.
Monitoring Existing Kidney Problems
For people with diabetes, hypertension, or known kidney disease, eGFR helps track how quickly kidney function is changing.
Guiding Treatment Decisions
Certain medications need dose adjustments when kidney function declines. eGFR helps determine safe drug doses.
Identifying the Need for Dialysis or Transplant
When eGFR drops below 15 mL/min/1.73 m², dialysis or kidney transplantation may be required.
Causes of Low eGFR (Reduced Kidney Function)
A low eGFR value means your kidneys are not filtering blood efficiently. Many conditions can lead to this reduction, such as:
Chronic Kidney Disease (CKD)
The most common cause of long-term low eGFR. CKD may result from diabetes, hypertension, autoimmune diseases, or structural abnormalities.
Diabetes Mellitus
High blood sugar damages the tiny blood vessels in the kidneys, gradually reducing filtration capacity.
Hypertension (High Blood Pressure)
Increased pressure damages kidney filters over time, leading to reduced eGFR.
Glomerulonephritis
Inflammation of the glomeruli (filtering units) decreases kidney filtration.
Polycystic Kidney Disease (PKD)
A genetic disorder where cysts develop in the kidneys, impairing function.
Urinary Tract Obstruction
Kidney stones, tumors, or prostate enlargement can block urine flow and reduce kidney performance.
Severe Dehydration
Lack of fluids temporarily lowers kidney filtration.
Long-Term Painkiller Use
Chronic use of NSAIDs can damage kidney tissue.
Recurrent Infections
Repeated kidney infections (pyelonephritis) can cause permanent scarring.
Symptoms of Low eGFR (Usually Below 60)
In early stages, kidney disease has few or no symptoms. As eGFR drops, the following symptoms may appear:
- Swelling in legs, ankles, or around the eyes
- Fatigue or persistent weakness
- Nausea or vomiting
- Loss of appetite
- Difficulty concentrating or mental fog
- High blood pressure
- Foamy or dark-colored urine
- Reduced urination
- Shortness of breath due to fluid buildup
When eGFR falls below 15, it typically indicates kidney failure, and dialysis or kidney transplant may be necessary.
Causes of High eGFR
A high eGFR reading is less common and often not harmful. Possible causes include:
Pregnancy
Kidney filtration increases during pregnancy, which can elevate eGFR temporarily.
Very Low Muscle Mass
People with low muscle mass produce less creatinine, which may falsely increase eGFR.
Overhydration
Taking in excessive fluids can dilute creatinine, resulting in a high eGFR.
High Protein Intake
Large protein meals may temporarily shift creatinine levels.
Laboratory or Calculation Error
Occasionally, improper sample handling or calculation issues may give a falsely high result.
Symptoms of High eGFR
There are typically no symptoms. High eGFR usually does not indicate disease unless linked to an underlying condition like pregnancy or muscle loss. If results seem unusual, your doctor may recommend repeating the test or using alternative assessments such as:
- Cystatin C test
- Creatinine clearance test
Reference (Normal) Range
The standard eGFR values used in clinical practice are:
≥ 90 mL/min/1.73 m²
Normal kidney function
60–89
Mild decrease; may be normal in older adults or early kidney disease
30–59
Moderate decrease — Stage 3 CKD
15–29
Severe decrease — Stage 4 CKD
< 15
Kidney failure (Stage 5 CKD); dialysis or transplant may be needed
These values may vary slightly depending on laboratory calculations or population factors.
Sample Type
- Sample Type: Serum (Blood Sample)
- Tube Used: Red Top (Plain Tube)
The test requires only a small blood sample and is often performed alongside creatinine, BUN, electrolytes, and urine tests.
Test Preparation
No fasting is required for an eGFR test. However, for the most accurate results:
- Avoid high-protein meals before the test
- Stay well-hydrated
- Avoid heavy exercise for 24 hours
- Inform your doctor about medications such as NSAIDs, diuretics, ACE inhibitors, or supplements like creatine
- Avoid alcohol before the test
Hydration and medication details are important because they can temporarily affect creatinine levels.
When to Consult a Doctor
You should seek medical advice if:
- Your eGFR is consistently below 60
- You have diabetes, high blood pressure, or a family history of kidney disease
- You notice swelling, fatigue, or urination changes
- Your urine test shows protein or blood
- You have recurring kidney stone symptoms
- You experience nausea, vomiting, or confusion along with abnormal eGFR
Your doctor may suggest further investigations such as kidney ultrasound, serum electrolytes, creatinine clearance, or urine ACR (Albumin-Creatinine Ratio).
Important Word Explanations
eGFR
Estimated Glomerular Filtration Rate — a calculated measure of kidney filtering capacity.
Creatinine
A muscle-waste product used to compute eGFR.
CKD
Chronic Kidney Disease — long-term damage affecting kidney function.
Dialysis
A medical treatment that removes waste and excess fluid when kidneys fail.
Polycystic Kidney Disease (PKD)
A hereditary disorder causing cyst formation in kidneys.
Glomerulonephritis
Inflammation of the kidney’s filtering units.
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