Estimated Glomerular Filtration Rate (eGFR) Test

The human body is a marvel of complex organs working together to function properly. One of the essential organs of the human body is its kidneys. These bean-shaped organs quietly perform vital functions, filtering waste and excess fluid from the blood. However, like any well-oiled machine, the kidneys can falter, leading to potentially serious consequences. The estimated glomerular filtration rate (eGFR) test assesses kidney function and disease progression. In this blog, we will understand what the eGFR test is, its importance, and the various results of this test.

What is an eGFR Test?

An eGFR test is a diagnostic tool used to gauge kidney function. It provides valuable insights into how efficiently our kidneys filter waste from the blood. Think of it as a measure of the kidney’s filtering capacity. To understand this test fully, it’s essential to grasp the concept of glomerular filtration rate (GFR) concept.

Glomerular Filtration Rate (GFR): eGFR Meaning

The glomerular filtration rate (GFR) refers to the rate at which blood is filtered by the glomeruli, the tiny blood vessels in the kidneys. It is a crucial indicator of kidney function because it reflects the kidneys’ efficiency in performing their primary function: filtering waste and excess fluids from the bloodstream to form urine. It is typically calculated based on blood creatinine levels, age, race, and gender and additional considerations like weight, height, and sex.

Now, why is monitoring the eGFR important? Simply put, it provides valuable insights into the health of your kidneys and can help detect kidney disease at an early stage.

eGFR and kidney function assessments are integral components of routine renal health screenings. The eGFR is typically reported in millilitres per minute per 1.73m² of body surface area and is often expressed as a percentage of normal. For example, if your eGFR is 100%, your kidneys are functioning at full capacity, whereas an eGFR of 0% indicates complete kidney failure.

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When is an eGFR Test Recommended?

Many people may not be aware of the risks lurking within their bodies. Chronic kidney disease (CKD) is a serious condition that can develop silently over time, often without noticeable symptoms until it reaches advanced stages. Healthcare professionals often recommend an eGFR test to identify and monitor CKD risk. Your healthcare provider may recommend an eGFR test if you have certain risk factors for chronic kidney disease, like the following:

  1. Diabetes: According to the CDC, people with diabetes are at a higher risk of developing kidney disease, making regular monitoring of kidney function essential. High blood sugar levels can damage the kidneys’ blood vessels and nephrons, leading to kidney damage over time. Nephrons, the tiny filters within the kidneys, are crucial in removing waste, controlling fluid balance, and filtering blood. Prolonged damage can result in thickening and scarring of the nephrons, compromising kidney function.
  2. Smoking: Smoking not only damages the lungs but also adversely affects kidney health in the following ways:
    • Decreasing Blood Flow: Smoking can damage the heart and blood vessels, leading to poor blood flow to the kidneys. This decreased blood flow can cause kidney damage over time.
    • Increasing Risk of Kidney Cancer: Smoking is linked to an increased risk of developing certain types of kidney cancer.
    • Causing Protein in the Urine: Smoking is associated with higher levels of protein in the urine, indicating kidney stress and potential damage.
    • Affecting Medications: Smoking can interfere with the effectiveness of medications used to treat high blood pressure, a significant risk factor for kidney disease.
  3. Family History: A family history of kidney disease, diabetes, or high blood pressure can predispose individuals to CKD. Shared genetic factors and familial lifestyle patterns may increase susceptibility to kidney disease within certain families.
  4. Age: According to this study by the NIH, being over 50 is considered a risk factor for CKD, highlighting the importance of proactive health screenings. As you age, the kidneys undergo natural changes, including a gradual decline in function. Additionally, age-related health conditions such as high blood pressure, diabetes, and heart disease can further exacerbate the risk of developing CKD. Regular health assessments, including eGFR testing, are essential for older adults to detect any early signs of kidney dysfunction and intervene promptly.
  5. Obesity: Excess weight strains the kidneys, increasing the risk of kidney disease. Overweight or obese people are more likely to develop conditions such as high blood pressure and diabetes, both of which are significant contributors to CKD. Furthermore, excess body fat can lead to inflammation and metabolic abnormalities, further compromising kidney function.

Furthermore, people with certain medical conditions or taking specific medications may also require eGFR testing to monitor kidney health. These conditions include congenital disabilities affecting kidney function, coronary artery disease, frequent urinary tract infections (UTIs), and high blood pressure.

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Factors Affecting eGFR Accuracy

eFFR accuracy can be influenced by many factors. While eGFR provides valuable insights into renal health, some factors affect its precision. These are:

  1. Age: Generally, older people tend to have lower eGFR values due to age-related changes in kidney function.
  2. Body Type: Extreme variations in body composition, such as being very overweight, highly muscular, morbidly obese, or having limb amputations, can impact eGFR accuracy. These conditions can alter the metabolic processes and filtration dynamics within the kidneys.
  3. Medications: Certain medications, including NSAIDs, PPIs, statins, antibiotics, diabetes drugs, antacids, herbal supplements, vitamins, and contrast dye, can all affect the accuracy of eGFR readings.
  4. Underlying Conditions: Pregnancy, cirrhosis, nephrotic syndrome, and a history of solid organ transplantation are among the factors that can distort eGFR accuracy. These conditions may directly affect kidney function or introduce complexities in the filtration process.
  5. Blood Lipids and BUN Levels: Elevated blood lipids and blood urea nitrogen (BUN) levels can influence eGFR readings. These biomarkers reflect metabolic and renal function, and deviations from normal ranges can affect the accuracy of eGFR calculations.
  6. Physical Activity: Less physical activity is associated with reduced eGFR values. Regular exercise promotes overall health and supports renal function, which in turn can improve eGFR accuracy.
  7. Creatinine Levels: eGFR is often derived from serum creatinine levels, but this approach may not always provide accurate results. Creatinine levels are influenced by muscle mass, dietary intake, and hydration status, leading to potential inaccuracies in eGFR estimation.

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Taking an eGFR Test

An eGFR test is a routine procedure, typically in a clinical setting, such as a doctor’s office, hospital, or laboratory. Here’s what you can expect during the process:

  1. Preparation: Before the test, your healthcare provider may advise you to fast for a certain period or refrain from certain medications, depending on the instructions provided. Follow these instructions carefully for accurate test results.
  2. Blood sample collection: The eGFR test requires a blood sample. First, a needle is inserted into a vein in your arm. Then, the healthcare professional will clean the site with an antiseptic solution. This minimises the risk of infection before inserting the needle. While some may experience mild discomfort during needle insertion, the procedure is generally well-tolerated.
  3. Laboratory analysis: Once the blood sample is collected, it is sent to a laboratory for analysis. In the lab, technicians will measure the creatinine levels in your blood. Creatinine levels are used in conjunction with other factors such as age, gender, and race to calculate the eGFR.
  4. Interpretation of results: After the analysis is complete, you will get your results. The eGFR normal range typically ranges from 90 to 120 mL/min/1.73 m², although this may vary depending on individual factors. Lower eGFR values may indicate decreased kidney function and may warrant further evaluation and management.

When undergoing an eGFR test, there are several special instructions and considerations to keep in mind:

  1. You may be instructed to fast for a certain period before the test.
  2. Adequate hydration is essential for optimal blood flow and sample collection.
  3. Inform your healthcare provider about any medications you currently take, including prescription, over-the-counter, and supplements.
  4. Be prepared for mild discomfort. If you have a fear of needles or experience significant anxiety about the procedure, inform your healthcare provider beforehand so they can provide appropriate support and guidance.
  5. Discuss any underlying health conditions requiring special considerations when interpreting eGFR results.
  6. Depending on your eGFR results and health status, your healthcare provider may recommend follow-up testing or additional evaluations.

Remember to communicate openly with your doctor about any concerns or questions regarding the test or your kidney health.

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Understanding eGFR Test Results: eGFR Interpretation

Your eGFR score indicates how well your kidneys filter waste from your blood, with lower scores suggesting decreased kidney function. Here’s what different eGFR levels signify and what they mean for your health.

Stage 1: GFR of 90+

A GFR of 90 or higher is typically considered normal in most healthy people. At this stage, there are usually no noticeable symptoms of kidney disease. Any deviation from the normal range for eGFR may indicate potential kidney dysfunction and requires further evaluation.

Stage 2: GFR of 60 to 89

A GFR between 60 and 89 may still be normal for specific demographics, such as older adults or infants, as long as no kidney damage is present. However, if this reduced kidney function persists for three months or longer alongside evidence of kidney damage, it indicates early chronic kidney disease (CKD). Similar to stage 1, symptoms might not be apparent, emphasising the importance of regular check-ups and monitoring.

Stage 3: GFR of 30 to 59

At stage 3, individuals have moderate CKD and may benefit from consulting a nephrologist, a doctor specialising in kidney care. A GFR in the range of 30 to 59 can lead to complications such as anaemia, early bone disease, and high blood pressure. While symptoms may still be subtle, medical intervention and lifestyle modifications become increasingly important at this stage to slow down the progression of kidney disease and manage associated conditions.

Stage 4: GFR of 15 to 29

Stage 4 signifies severe CKD, with a GFR falling between 15 to 29. At this point, the kidneys have significantly impaired function, and individuals are at high risk of requiring dialysis or a kidney transplant in the future. Patients at this stage must work closely with their healthcare team to discuss treatment options, manage symptoms, and prepare for potential interventions like dialysis or transplantation.

Stage 5: GFR of 15 or less

Stage 5, or end-stage renal disease (ESRD), occurs when the kidneys have lost almost all ability to function, with a GFR of 15 or less. At this critical stage, individuals require immediate medical intervention in the form of dialysis or a kidney transplant to sustain life. Without these interventions, complications can become life-threatening.

Stage GFR Range Description
1 90+ Normal kidney function with few or no symptoms
2 60 to 89 Normal for some demographics, but may indicate early CKD if sustained for 3+ months with kidney damage
3 30 to 59 Moderate CKD, may lead to complications such as anemia, bone disease, and high blood pressure
4 15 to 29 Severe CKD, high risk of requiring dialysis or kidney transplant
5 15 or less End-stage renal disease (ESRD), requires immediate intervention with dialysis or kidney transplant.

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Other Tests Related To Kidney Function Evaluation

Other Tests Related To Kidney Function Evaluation

A holistic approach incorporating eGFR and complementary tests is essential for accurate kidney function evaluation. Additional tests along with the eGFR test for kidney function are:

Creatinine Test:

The creatinine test is one of the most common tests to evaluate kidney function. Healthy kidneys should efficiently remove creatinine, and hence, high creatinine levels in the blood mean impaired kidney function.

Creatinine Clearance:

Unlike the creatinine blood test, which measures the creatinine concentration in the blood, creatinine clearance involves collecting urine samples over a specific period to measure how efficiently the kidneys are clearing creatinine from the blood.

Blood Urea Nitrogen (BUN) Test:

The blood urea nitrogen (BUN) test measures the amount of urea nitrogen in the blood. Urea is a waste product formed when the body breaks down proteins. Elevated BUN levels may indicate impaired kidney function since the kidneys filter urea from the blood.

Creatinine-Urine Test:

The creatinine-urine test evaluates how much creatinine is excreted in the urine over a specific period. Abnormal creatinine levels in urine can indicate various kidney disorders, such as glomerulonephritis or kidney tubule defects.

These additional tests offer complementary information that can aid in diagnosing and monitoring kidney disorders. For example, while eGFR estimates kidney function based on serum creatinine levels, creatinine clearance and urine creatinine tests directly measure how effectively the kidneys are clearing creatinine. Similarly, the BUN test provides insights into the body’s nitrogen balance and can help assess overall kidney function.

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The eGFR test helps you to identify any kidney disease. Remember, early detection and intervention are vital in preserving kidney function and preventing complications associated with kidney disease. So, stay proactive about your health. Pay attention to your doctor’s recommendations regarding regular screenings, including the eGFR test, to ensure your kidneys function at their best. By staying informed and proactive, individuals can take steps to preserve kidney function and maintain their quality of life.

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FAQ’s (Frequently Asked Questions)

What is a normal eGFR level?

A normal eGFR is greater than 90. Values as low as 60 are also considered normal as long as there is no other evidence of kidney disease. The test result is often shown as a percentage of normal because people find it helpful to think of kidney function as a percentage. 100%  would mean a fully functioning kidney, and 0% would imply a non-functioning kidney.

What is the eGFR?

eGFR (estimated glomerular filtration rate) is a measure of how well your kidneys are working.

How do you calculate eGFR?

eGFR can be calculated using the formula: eGFR = (Serum Creatinine * µmol/L) / Age * (mL/min/1.73m²). Alternatively, it can be calculated using an eGFR calculator.

Is eGFR 70 normal?

Yes, an eGFR of 70 is within the normal range.

Can drinking more water improve GFR?

Staying hydrated can improve GFR somewhat, but consulting with a healthcare professional for personalised advice is essential.

Is a GFR of 120 good?

A GFR of 120 is above the normal range, which is typically between 90 and 120 mL/min/1.73m².

What foods increase GFR?

Foods generally considered beneficial for kidney health and may help improve GFR include those rich in antioxidants and omega-3 fatty acids. The food must be low in sodium, potassium, and phosphorus. Examples include fruits, vegetables, and lean proteins.

Is low eGFR normal?

A low eGFR may indicate reduced kidney function. Still, it’s essential to interpret the result in the context of other factors and consult with a doctor for proper evaluation.

How accurate is the eGFR test?

The eGFR test is generally considered accurate for estimating kidney function, but it’s essential to recognise that it is an estimate and not a direct measure. Age, race, and muscle mass can influence its accuracy.

Last Updated on by Dr. Damanjit Duggal 


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