Summary

• The eGFR can show how well your kidneys are filtering your blood.
• It is a calculation that represents the amount of blood filtered per minute.
• eGFR stands for the estimated glomerular filtration rate.
• The glomeruli are the tiny filters in your kidneys.
• The higher the eGFR, the better your kidneys are working.

What is the glomerular filtration rate (GFR)?

The glomerular filtration rate (GFR) is a measurement of how well your kidneys are working. Your kidneys filter waste and excess fluid from your blood and the glomeruli are the tiny filters in your kidneys that do this.

They filter your blood and remove wastes and excess fluid from your body which are disposed of as urine. For more on the way your kidneys work, and the other tests used to assess them see Kidney function tests.

If your kidneys are not working properly, waste products build up in your blood and the chemical balance is disturbed. Levels of the electrolytes your body uses for daily function - sodium, potassium, phosphate and calcium - are not regulated properly. This can lead to serious health issues. Fluid levels can increase to dangerous levels, causing damage and serious health problems.

What is the estimated glomerular filtration rate (eGFR)?

In the early stages of chronic kidney disease (CKD) there are usually no obvious symptoms, yet it is important to be able to diagnose kidney disease as early as possible. Further damage can be prevented through treating high blood pressure, diabetes or other diseases that can damage the kidneys.

If you are known to be at risk of CKD, you need to be monitored regularly to make sure your kidneys are healthy. Finding out how well your glomeruli are filtering your blood is an important part of this.

Measuring the glomerular filtration rate (GFR) is considered the best single measure of kidney function. However, it is a complicated and lengthy process which makes it impractical to perform other than for research or transplant purposes.

In order to be able to decide on the GFR easily, as a routine test that can be ordered regularly, laboratory scientists use a formula to estimate it. This is the estimated glomerular filtration rate, or eGFR.

eGFR is very accurate and convenient way to detect changes in kidney function. The formula uses results from a creatinine blood test with personal information such as your age and gender.

Creatinine is a waste product which is released into your blood when muscles are used and muscle tissue breaks down. Almost all creatinine is removed by the kidneys. However, if you have kidney disease, creatinine in the blood gradually builds up.

Why get tested?

The eGFR helps detect kidney damage early so that steps can be taken to stop or slow the progression of kidney damage. People who are at a greater risk of kidney disease include those with diabetes, blood vessel disease, heart problems, high blood pressure, First Nations Australian aged 18 years and over, blockages to urine flow and people taking some commonly prescribed drugs including diuretics (water tablets) and medications that treat high blood pressure.

Often, CKD does not have any symptoms until the later stages. This is the reason why reliable estimates of GFR are so important for identifying CKD as early as possible.

If kidney damage is detected early, your medical team may need to know your eGFR before prescribing certain medications, because you may need a lower dose than usual if you have kidney damage.

As well as periodic monitoring, the eGFR might be repeated if your health care provider feels that a temporary condition may be affecting your results.

If you are considered at risk for kidney disease you may also be monitored with a test that measures small amounts of albumin in your urine using an albumin-creatinine ratio also known as the microalbumin test. The presence of albumin and other plasma proteins as well as blood in the urine can all be signs of potential kidney damage.

How is the eGFR calculated?

To decide on your eGFR, a standardised eGFR calculation has been adopted by all Australian laboratories. This is the CKD-EPI. The CKD-EPI stands for Chronic Kidney Disease Epidemiology Collaboration. It uses an equation that considers your:

• age
• sex at birth
• the levels of creatinine in your blood. A higher level of creatinine in the blood will result in a lower eGFR.

A calculation of GFR using the CKD-EPI formula is available through Kidney Health Australia.

Having the test

Sample

Blood

Preparation

In most cases, you do not need to fast for an eGFR test. The test measures creatinine levels in your blood, which are not significantly affected by food intake but in certain health conditions your doctor may ask you to fast to get a more accurate result.

Your results

eGFR is reported as a number that reflects the percentage of kidney function you have. The lower your eGFR number the less well your kidneys are working.

• Normal eGFRs are usually over 90. If your eGFR is between 60 and 90 in at least two blood tests over three months, your kidney function is considered normal or near normal.
• A result below 60 suggests some loss of kidney function. For a diagnosis of chronic kidney disease, you need to have either an eGFR of less than 60 on two to three tests over three months and/or signs of kidney damage.
• Some blood pressure medications can affect your eGFR results.
• Increased body fluids during pregnancy can affect your eGFR results.
• The eGFR is calculated on a standard body size. If you have a small build or are frail or if you have a very large build, such as a body builder, your results may need to be adjusted.
• Results from the eGFR can show whether you have kidney disease, but they cannot show the cause. You will need other tests for that.
• Sometimes, in very early kidney damage, especially when the kidneys are damaged by diabetes, other tests such as an albumin-creatinine ratio test may show kidney damage before any change in the eGFR.

Questions to ask your doctor

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods, medications or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

More information

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

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