What are kidney function blood tests?

Kidney function blood tests are a group of blood tests that check how well your kidneys are working.

Your kidneys are 2 small organs located below your ribs on either side of your spine. They are part of your urinary system. Their main job is to clean your blood by removing waste products and extra fluid, which then exits your body as urine (wee).

Your kidneys are important for eliminating waste and keeping the right balance of fluids, electrolytes and minerals. If your kidneys stop working properly, waste products and fluid can build up to dangerous levels. This may lead to kidney damage and serious health problems.

Kidney function tests (also called renal function tests) measure substances in your blood, including:

• electrolytes — sodium, potassium, chloride and bicarbonate
• waste products — urea and creatinine. Your creatinine result is used to calculate your eGFR (estimated glomerular filtration rate). This is a measurement of how well your kidneys filter waste from your blood.

In some situations, your doctor may also request tests for protein and glucose levels in your blood. These tests can help them get a better picture of your overall kidney and general health.

Your doctor may refer you for a urine test (urinalysis) at the same time as a kidney function blood test. These tests can be interpreted together to give a better picture of your kidney health.

Learn more about urine tests.

When are kidney function blood tests used?

Kidney function tests can help check for kidney disease. They can also help monitor kidney disease over time and check your response to treatment.

Your doctor may refer you for these tests if you:

• have kidney disease
• have conditions that increase your risk of kidney disease, such as high blood pressure, heart disease or diabetes
• have a family history of kidney disease
• take medicines that could affect your kidneys
• have been exposed to substances that could harm your kidneys
• have had symptoms such as vomiting or diarrhoea — these can affect your fluid levels, electrolyte levels and your kidneys

Where can I get a kidney function blood test?

You usually need to go to a pathology collection centre with a referral from your doctor. Your doctor will recommend one near you.

Sometimes, your doctor will collect blood for testing in their clinic. Blood tests are also routinely done in hospitals.

How do I prepare for a kidney function blood test?

Check with your doctor if fasting is needed and for how long.

If your eGFR is being tested, avoid eating cooked meat for 4 to 6 hours before the test, as this can raise your creatinine level (which is used to calculate your eGFR).

If you are having other blood tests or a urine test done at the same time, there may be more instructions. Ask your doctor or the pathology collection centre if you need to do anything before your test.

What happens during a kidney function blood test?

A health professional will take a sample of blood, usually from a vein in your arm. The blood will then be sent to a laboratory for testing.

What do my kidney function results mean?

Your results show how well your kidneys filter waste products and keep the right balance of important substances in your body.

• Abnormal levels of electrolytes and minerals may signal kidney problems or another medical condition.
• High levels of waste products urea and creatinine may suggest reduced kidney function or dehydration.
• eGFR (estimated glomerular filtration rate) is measured using your creatinine result. A lower result may suggest reduced kidney function or kidney failure.

There can be many potential reasons for abnormal results, so it's important to discuss your results with your doctor to understand what they mean for you.

If the cause of your results isn't clear, your doctor may suggest more tests to identify the cause.

Resources and support

Pathology Tests Explained has information about kidney function tests.

Read our 'Guide to blood testing' to learn more about blood tests, including:

• what to consider before having the test
• what happens during a blood test
• how accurate results are
• blood test costs

You can also call the healthdirect helpline on 1800 022 222 (known as NURSE-ON-CALL in Victoria). A registered nurse is available 24 hours a day, 7 days a week.