Estimated Glomerular Filtration Rate (eGFR) Test

What to expect when undergoing this test

An estimated glomerular filtration rate (eGFR) test is a blood test that’s used to figure out how well your kidneys are doing their job. The test measures the amount of creatinine in your blood and, using a formula, mathematically derives a number that estimates how well your kidneys are functioning. The formula uses your creatinine levels, age, sex, weight, and race to arrive at that number—your eGFR.

Purpose of Test

Your doctor will order an eGFR test if he suspects you have chronic kidney disease. So, if you complain about having symptoms of kidney disease, your doctor may order you to take an eGFR test. These symptoms include:

  • Dry and persistently itchy skin
  • Muscle cramps
  • Swollen ankles and feet
  • Increase in frequency of urination
  • Foamy or bloody urine
  • Sleep problems
  • Fatigue and low energy levels
  • Concentration problems
  • Nausea and vomiting
  • Poor appetite
  • High blood pressure

Early-stage kidney disease doesn't normally have any symptoms. Because of this, if you have any preexisting condition like diabetes, high blood pressure, and cardiovascular disease—all of which tend to affect your kidneys—your doctor will likely order this test for you at regular intervals. A family history of kidney disease could also necessitate this test.

Further, if you’ve already been diagnosed with kidney disease, your doctor will likely still order an eGFR test regularly to monitor how well your kidneys are faring.

The main function of your kidneys is to clean your blood. The glomeruli, tiny filters found in your kidneys, are central to this job. So, your eGFR rate is actually how much blood these glomeruli filter per minute, and it works by measuring the levels of creatinine in your blood.

Creatinine is one of the types of waste that the kidneys help to filter out of the body. Therefore, if a high level of creatinine is found in your blood, it might signal that your kidneys (the glomeruli, in particular) aren't doing a good job of filtering and cleaning out your blood.

Limitations

The eGFR test is not 100 percent accurate and it can only give an estimate of your filtration rate. Additionally, the standard formula for calculating eGFR is not valid for people under the age of 18.

An eGFR test is usually ordered alongside a urine test for albumin to diagnose kidney disease. In the same vein, just as eGFR tests are used to monitor kidney disease, urine tests for albumin are generally used concurrently for the same purpose.

Albumin is a protein that’s normally found in your blood, and properly functioning kidneys do not allow it to get into your urine. However, damaged ones do. So if the results of this test show that there's albumin in your urine, there’s a high chance you have kidney disease. Albumin in the urine is called albuminuria.

A urinalysis may also be ordered to enable the doctor to check for any signs of kidney damage in your urine.

More Kidney Function Tests and What They Mean

Risks and Contraindications

There are generally no risks or contraindications associated with eGFR testing.

Before the Test

You can expect to discuss your symptoms with your doctor, as well your family history of kidney disease (if any).

You should disclose all medications you are taking to your doctor. This is because certain drugs can interfere with eGFR results because they increase your creatinine levels. Some of these drugs are cisplatin and gentamicin.

You should expect to discuss your medical history and if you have conditions like diabetes and high blood pressure, you should disclose that too.

Disclose if you are pregnant or if there's any chance you may be, as this can affect the test results.

Timing

Because the test takes the form of a blood test, it will just take a few minutes.

Location

The test will take place in the hospital.

What to Wear

You can dress however you want for this test. However, keeping in mind that the blood will be drawn from your arm, it may be better for you to wear sleeveless clothes or clothes with which uncovering your arm will be easy.

Food and Drink

Your doctor may or may not instruct you to not eat anything on the day of the test or to avoid certain foods. He may also instruct you to stop taking certain medications.

During the Test

A needle will be inserted into the skin on your arm and your blood will be drawn. You may feel a moderate amount of pain or merely a sting, and the entire process will probably take under a minute to complete.

After the Test

You will be allowed to go home immediately, and your doctor (or the technician who attended to you) will tell you when to return for your test results.

You will be instructed to report back to the hospital if you notice any bleeding or serious bruising at the site where the needle was inserted.

Side Effects

There are some very common side effects of undergoing a blood test like eGFR. You shouldn’t worry if you experience any of these side effects and can expect them to go away very soon:

  • Slight bruising or swelling
  • Slight stinging or throbbing
  • Feeling lightheaded or dizzy

However, serious and rare side effects of having your blood drawn are:

  • Excessive bleeding
  • Infection
  • A swollen area filled with blood. This is also called a hematoma.

You should report back to your doctor immediately if you any experience any of these.

Interpreting Results

Your eGFR result will be a number and this is what each range of numbers means:

  • GFR 90 and above: You have normal to high kidney function.
  • GFR 60–89: There is a mild reduction of kidney function. This does not mean you have kidney disease. It is only when there are other signs of kidney damage that this GFR number may signify kidney disease.
  • GFR 45–59: There is mild to moderate reduction in kidney function, and it may signify that you have kidney disease.
  • GFR 30–44: This shows that there is a moderate to severe reduction of kidney function.
  • GFR 15–29: This signifies a severe reduction of kidney function.
  • GFR 15 or less: This signifies kidney failure and you will need to be on dialysis or get a kidney transplant.

This being said, it is only your doctor that can give you the most accurate interpretation of your results based on your eGFR result and other individual symptoms, complications, and medical history.

You should also note that your eGFR test result can be influenced by many factors. This means that you may not get a correct eGFR result if:

  • You’re pregnant
  • You’re under the age of 18
  • You’re elderly, as you’re likely to have a low eGFR if you’re elderly because GFR normally declines with age
  • You’re on a vegan or vegetarian diet
  • You’re significantly more or less muscular than the average person

Accordingly, your doctor will look at these things, if any apply to you, before making a diagnosis of chronic kidney disease (CKD), or ordering further tests to confirm the diagnosis.

How Chronic Kidney Disease Is Diagnosed

Follow Up

Depending on your eGFR test result and other surrounding medical information, your doctor may not make a definitive diagnosis of kidney disease. Instead, he/she may ask you to come back for another eGFR test to check if the result remains the same.

If you’ve been diagnosed with kidney disease from your eGFR test results, your doctor may order the following tests for you:

  • Kidney biopsy: This test involves taking a small price of your kidney for microscopic examination. This is done in order to determine the exact type of kidney disease you have, and how far the disease has progressed so that an appropriate treatment plan can be devised.
  • Ultrasound or CT Scan: Either of these imaging tests may be ordered so that your doctor can get a clear picture of your kidneys, and determine what state they’re in.

In addition to this, your doctor may also refer you to a nephrologist—a doctor that specializes in kidney problems—to determine the next steps and help manage your condition.

It is extremely necessary to have an open and detailed conversation about your eGFR result with your doctor. If you’d like, you can also opt to take the test in another hospital or seek out a second medical opinion on your initial diagnosis.

A Word From Verywell

It is impossible to reduce your eGFR, you can only keep it from reducing. So, regardless of what your eGFR test results are, it’s important to make healthy lifestyle choices. Eating healthy, quitting smoking and being physically active are some of the things you can do to make sure this doesn’t happen. If you’re particularly at risk of developing kidney disease, you should set up a regular schedule to get your GFR checked.

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