Estimated Glomerular Filtration Rate - Purpose, Procedure, Results Interpretation, Normal Values and more

Estimated Glomerular Filtration Rate (eGFR) is a key measurement used to assess kidney function and determine how well the kidneys are filtering waste from the bloodstream. This important test helps doctors evaluate the risk of chronic kidney disease (CKD) and monitor kidney health over time. The eGFR is a calculation based on factors such as age, gender, race, and serum creatinine levels, which can indicate early signs of kidney problems, even before noticeable symptoms appear.

What is the Estimated Glomerular Filtration Rate (eGFR)?

Estimated Glomerular Filtration Rate (eGFR) is a blood test that measures the efficiency of the kidneys in filtering waste products from the blood. It specifically calculates how much blood passes through the glomeruli, the tiny filters in the kidneys, each minute.

The eGFR is an estimate, which is why it includes factors such as serum creatinine levels, age, gender, and race to provide a more accurate measure of kidney function. Serum creatinine is a waste product of muscle metabolism that is normally filtered by the kidneys. Elevated creatinine levels can indicate impaired kidney function.

eGFR is often used as an indicator of kidney health, and it is essential for diagnosing and staging chronic kidney disease (CKD). It is also useful in tracking the progression of kidney function in patients with known kidney disease.

How is eGFR Measured?

The eGFR is calculated using a formula that factors in your serum creatinine levels along with age, sex, and sometimes race. The most common formula used to estimate eGFR is the Modification of Diet in Renal Disease (MDRD) Study equation, though more recently, the CKD-EPI equation has gained popularity for providing more accurate results in certain populations.

Here’s an outline of how the eGFR is measured:

1. Serum Creatinine Test: A blood sample is drawn from the patient to measure the serum creatinine level, which is a key waste product filtered by the kidneys.
2. Application of a Formula: The serum creatinine level is then used in a formula (either the MDRD or CKD-EPI equation) that also includes the patient’s age, sex, and race to calculate the eGFR.
3. Interpretation: The calculated eGFR provides an estimate of how well the kidneys are filtering waste from the bloodstream, with lower values indicating impaired kidney function.

Normal Range for eGFR

The normal range for eGFR depends on various factors such as age, sex, and race. However, in general, the eGFR should be greater than 90 mL/min/1.73m² for healthy individuals, with values typically decreasing slightly with age.

Breakdown of eGFR ranges:

• Above 90 mL/min/1.73m²: Normal kidney function (no evidence of kidney disease).
• 60-89 mL/min/1.73m²: Mildly decreased kidney function, but no significant kidney damage. Monitoring is usually recommended.
• 30-59 mL/min/1.73m²: Moderate kidney damage or impairment, requiring closer monitoring and potential interventions.
• 15-29 mL/min/1.73m²: Severe kidney damage, often requiring advanced care, including medications or dialysis preparation.
• Below 15 mL/min/1.73m²: Kidney failure, requiring dialysis or a kidney transplant.

It’s important to note that eGFR values are estimates and that other tests or assessments may be needed to confirm kidney health.

Uses of eGFR

The Estimated Glomerular Filtration Rate (eGFR) is primarily used to assess kidney function, identify kidney disease, and track the progression of kidney damage. Below are the main uses of eGFR:

1. Screening for Chronic Kidney Disease (CKD): The eGFR is a valuable tool in screening for CKD, particularly in high-risk populations such as those with hypertension, diabetes, or a family history of kidney disease.
2. Diagnosing Kidney Disease: By comparing eGFR results to normal values, doctors can diagnose kidney dysfunction. It is particularly useful for detecting early-stage kidney disease before symptoms appear.
3. Assessing the Severity of Kidney Disease: Once CKD is diagnosed, the eGFR helps stage the disease (from stage 1 to stage 5) and monitor the progression over time.
4. Monitoring Kidney Function in At-Risk Patients: Individuals with diabetes, hypertension, or other conditions that may affect kidney function are routinely monitored for changes in eGFR to identify early signs of kidney impairment.
5. Guiding Treatment Decisions: eGFR values help guide decisions regarding treatment options, such as adjustments in medications, lifestyle changes, and in some cases, the need for dialysis or a kidney transplant.
6. Assessing Medication Dosage: Many medications are eliminated by the kidneys. In patients with impaired kidney function, eGFR is used to adjust the dosage of certain medications to prevent toxicity.

How to Prepare for the eGFR Test

The eGFR test is relatively simple and requires minimal preparation. Here’s what to expect:

• Fasting: There is generally no need to fast before an eGFR test. However, it’s always important to follow the specific instructions provided by your healthcare provider.
• Hydration: Staying hydrated can help ensure that your kidney function is assessed accurately. Drinking plenty of water before the test is recommended, unless otherwise instructed by your doctor.
• Medications: Inform your healthcare provider about any medications or supplements you are taking. Some medications, particularly those that affect kidney function, may need to be adjusted prior to the test.
• Blood Test: The eGFR is based on a blood test measuring the serum creatinine level. A healthcare professional will draw a blood sample for analysis.

Interpreting eGFR Results

The interpretation of eGFR results is crucial in understanding kidney function. Here’s how to interpret your eGFR results:

• Normal eGFR (Above 90 mL/min/1.73m²): A normal eGFR suggests that the kidneys are functioning properly, and there is no indication of kidney disease. However, further tests may still be required if you have symptoms or risk factors.
• Mild Decrease (60-89 mL/min/1.73m²): If your eGFR is in this range, it may indicate early kidney damage, but further testing is often necessary to monitor the situation. Lifestyle changes or medications may be recommended to protect kidney function.
• Moderate Decrease (30-59 mL/min/1.73m²): Moderate kidney dysfunction is a concern and requires further evaluation. Close monitoring, along with lifestyle modifications and medications, may be required to prevent progression to more severe stages.
• Severe Decrease (15-29 mL/min/1.73m²): At this stage, kidney function is severely compromised, and advanced treatment options like dialysis or preparation for a kidney transplant may be necessary.
• Kidney Failure (Below 15 mL/min/1.73m²): A very low eGFR indicates kidney failure, where the kidneys are no longer able to perform their essential functions. Dialysis or a kidney transplant will likely be required.

Risks and Benefits of eGFR

Benefits:

• Early Detection: eGFR helps detect kidney dysfunction in its early stages, even before symptoms appear, allowing for early intervention.
• Monitoring Disease Progression: Regular eGFR tests can track the progression of kidney disease and help adjust treatments accordingly.
• Non-Invasive: eGFR is a simple blood test that does not require any invasive procedures.

Risks:

• Inaccuracy: eGFR is an estimate and may not be entirely accurate in individuals with certain medical conditions, such as extreme muscle mass loss or obesity.
• False Results: Conditions such as pregnancy, dehydration, or taking specific medications can affect the accuracy of eGFR results.

Frequently Asked Questions (FAQs)

1. What is eGFR?

eGFR is an estimated measurement of kidney function. It helps doctors assess how well your kidneys are filtering waste from your blood, which is critical for diagnosing kidney disease.

2. How is eGFR calculated?

eGFR is calculated based on your serum creatinine levels, age, sex, and sometimes race. A healthcare provider will use these factors to determine your kidney function.

3. How is eGFR related to kidney disease?

An eGFR of less than 60 mL/min/1.73m² over three months indicates potential kidney disease, while values below 15 mL/min/1.73m² suggest kidney failure.

4. How accurate is eGFR?

eGFR is an estimate and may not be completely accurate in individuals with extreme body types or certain medical conditions. Additional tests may be required for a more precise diagnosis.

5. Why do I need an eGFR test?

eGFR is used to screen for kidney disease, monitor kidney function in people with conditions like diabetes or hypertension, and guide treatment decisions.

6. What does it mean if my eGFR is low?

A low eGFR indicates that your kidneys may not be filtering waste as efficiently as they should. This could suggest kidney damage, and further tests or monitoring may be needed.

7. How can I improve my eGFR?

Maintaining a healthy diet, controlling blood sugar and blood pressure, staying hydrated, and avoiding smoking and excessive alcohol can help protect kidney function.

8. What is the normal range for eGFR?

A normal eGFR is typically above 90 mL/min/1.73m². However, eGFR naturally decreases with age, and slight decreases may not always be concerning.

9. Is eGFR the only test to assess kidney health?

While eGFR is a critical indicator of kidney function, other tests, such as urine albumin, kidney imaging, and biopsy, may be used to provide a comprehensive assessment.

10. Can I get eGFR from a home test kit?

Currently, eGFR requires a blood sample and should be tested by a healthcare professional. Home tests may measure creatinine levels but cannot calculate eGFR accurately without additional information.

Conclusion

The Estimated Glomerular Filtration Rate (eGFR) is a vital test that provides insights into kidney function and helps diagnose early stages of kidney disease. By measuring how efficiently the kidneys are filtering waste, eGFR helps doctors track kidney health, monitor disease progression, and guide treatment decisions. Whether you have diabetes, hypertension, or are simply monitoring your kidney function, understanding the eGFR test and its results can empower you to take proactive steps toward preserving kidney health. If you have concerns about your kidney function or risk factors for kidney disease, speak with your healthcare provider about scheduling an eGFR test.