Estimated Glomerular Filtration Rate (eGFR)

What is estimated glomerular filtration rate?

Estimated glomerular filtration rate (eGFR) is an estimated calculation of how well your kidneys work. It’s based on a blood test that measures the creatinine (or cystatin C). Your kidneys contain glomeruli. Glomeruli are groups of tiny blood vessels that help remove toxins (waste) from your blood. Your eGFR measures how well the blood is cleaned by the glomeruli in 1 minute.

Your estimated glomerular filtration rate helps healthcare providers spot problems with your kidneys, including chronic kidney disease (CKD). When you have CKD, your glomeruli aren’t filtering the blood appropriately. That causes dangerous toxins to build up in your blood.

When do healthcare providers calculate eGFR?

When you have a blood test as part of a routine checkup, eGFR is often part of the basic metabolic panel. A healthcare provider may also check your eGFR to help determine if you have chronic kidney disease and, if you do, how severe it is.

A provider may also use your eGFR to monitor your kidney health if you have or take medications to treat the following:

• Biological family history of CKD
• A body mass index (BMI) greater than 25 (have overweight/obesity)
• Congenital conditions (conditions you have at birth) that affect kidney function
• Diabetes
• Frequent urinary tract infections (UTIs) or blockages in your urinary system
• Heart disease, including coronary artery disease
• High blood pressure (hypertension)
• Transplant

How do healthcare providers determine eGFR?

Healthcare providers use a formula to estimate your glomerular filtration rate. They calculate your eGFR value from the serum (blood) creatinine or cystatin C in your blood sample, along with your:

• Age
• Sex
• Height
• Weight

Your body makes and uses creatine to provide energy to your muscles. When your muscles use this energy, the muscle tissue breaks down and the creatine turns into creatinine, which gets into your blood. Healthy kidneys filter creatinine out of your blood, and your body gets rid of it when you urinate (pee). If you have CKD, creatinine stays in your blood and may gradually build up.

Providers sometimes measure cystatin C levels in your blood if your creatinine results aren’t conclusive. Cystatin C is a small protein that your body’s cells make. Your age, muscle mass and/or diet may affect your creatinine levels. But these factors don’t affect your cystatin C levels. If you’re over 65 or have a lot of muscle mass, your cystatin C levels may more accurately indicate your kidney function than your creatinine levels.

How do I prepare for the test?

An eGFR blood test is very sensitive, especially for a creatinine blood test. You may not get an accurate eGFR if you don’t follow the healthcare provider’s guidelines to prepare for the test. These may involve:

• Fasting (drinking only liquids and avoiding solid foods)
• Not taking certain medications
• Avoiding meat for a day or two before your test

You may not get an accurate eGFR if you don’t follow the provider’s guidelines.

What to expect during the test

eGFR is usually part of a routine blood test. A healthcare provider typically draws blood from a vein in your arm. They then send your blood sample to a lab for analysis.

Let the provider know if you’re afraid of needles. They can suggest ways to help you relax before taking your blood sample

What to expect after

After taking your blood sample, the provider will put a bandage on the spot where the needle went in. They may suggest that you rest for a few minutes before you stand up and leave. Once they determine you’re OK, you can go home.

What are the risks of an eGFR blood test?

An eGFR blood test is very safe. Common side effects include:

• Pain at the injection site
• Bleeding
• Bruising

There’s also a small chance of:

• Fainting
• Infection

What do eGFR numbers mean?

For adults, a normal eGFR is about 100. The lowest eGFR is 0, which means your kidneys aren’t working. A healthcare provider may diagnose chronic kidney disease if your eGFR stays below 60 for three months.

Your eGFR will decrease as you age, even if you don’t have kidney disease. The chart below indicates a normal range for eGFR according to your age.

What stage of eGFR is kidney failure?

There are five stages of chronic kidney disease. Stage V CKD is a sign of kidney failure.

• Stage I: Your eGFR is higher than 90 but below 100. At this stage, you have mild kidney damage, but your kidneys are working well.
• Stage II: Your eGFR may be as low as 60 or as high as 89. You have an increase in kidney damage from stage I, but your kidneys still work well.
• Stage III: Your eGFR may be as low as 30 or as high as 59. You may have mild or severe loss of kidney function and may experience symptoms.
• Stage IV: Your eGFR may be as low as 15 or as high as 29. You have severe loss of kidney function.
• Stage V: Your eGFR is below 15. It means you have less than 15% kidney function. It’s the most serious stage and is life-threatening without dialysis or a kidney transplant.

When should I know the results of an eGFR blood test?

You should get the results of an eGFR blood a few days after your blood draw.

If the results are abnormal, what are the next steps?

A healthcare provider may recommend additional tests if your eGFR blood test results are abnormal. These may include:

• Urinalysis (pee test): A pee test helps detect early signs of kidney disease, such as the presence of the protein albumin or blood in your pee (hematuria).
• Kidney ultrasound or CT scan: These imaging tests help identify problems in your urinary system that may happen alongside CKD, such as kidney stones and kidney cancer.
• Creatinine clearance test (24-hour pee collection): A creatinine clearance test measures creatinine levels in your pee and blood at the same time.
• Kidney biopsy: A kidney biopsy helps a provider determine the type and severity of kidney disease.

When should I call my doctor?

Call a healthcare provider if you have kidney disease or risk factors, such as:

• Peeing more than usual
• Dry skin
• Itchy skin
• Darkening of your skin
• Muscle spasms
• Nausea and vomiting
• Shortness of breath
• Swelling in your hands, feet or ankles

When should I worry about eGFR?

You likely have chronic kidney disease if you’ve had an eGFR of 60 or lower for more than three months. You may also have CKD if your eGFR is above 60 and you have signs of kidney damage.

Should I worry if my eGFR is 75?

It depends on your age and other factors. A mildly low eGFR doesn’t definitively mean you have kidney disease. But having a healthcare provider check your eGFR regularly is a good idea.

What is measured glomerular filtration rate (mGFR)?

eGFR gives a general estimate as to how well your kidneys work. Healthcare providers can precisely measure your glomerular filtration rate, but the tests are complex. Because of this, providers typically only use measured glomerular filtration rate (mGFR) for research or kidney transplant purposes.