Erythrocyte sedimentation rate (ESR) blood test

An erythrocyte sedimentation rate (ESR) blood test checks how fast red blood cells sink to the bottom of a test tube. If they fall faster than normal, it may mean there is inflammation in your body.

Inflammation is your body's response to injury, irritation or infection.

Your doctor may order an ESR blood test along with other tests to check for:

• infection
• conditions that cause inflammation, such as an autoimmune disease
• some types of cancer

This blood test does not show the exact cause or location of a problem. Other tests are needed to find the location and cause of the inflammation, infection or cancer.

ESR blood tests are especially useful for detecting conditions including:

• giant cell arteritis (inflammation of blood vessels)
• polymyalgia rheumatica (a condition causing muscle pain and stiffness)
• systemic lupus erythematosus (long-term autoimmune illnesses)

If you have one of these conditions, your doctor may also use ESR blood tests to monitor your response to treatment.

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.

There is no special preparation needed for an ESR blood test.

However, if you are having other blood tests done at the same time, you may need to prepare. Check with your doctor or the pathology collection centre if there is anything you need to do before your 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.

How does an ESR blood test work?

In an ESR test, the blood sample is placed into a tall, thin tube. The blood is allowed to settle and the 'sedimentation rate' is measured.

If there is inflammation, red blood cells stick to each other and form clumps. These clumps are heavier than normal red blood cells, so if there is inflammation, the red blood cells will clump together and fall more quickly to the bottom of the tube.

If there is no inflammation, the red blood cells will settle more slowly.

After some time, a layer of clear liquid (plasma, which has no red blood cells) forms at the top of the tube. The ESR measures the height of the clear plasma at the top of the tube.

A low ESR means that red blood cells settle slowly, which suggests there is no inflammation.

A high ESR means that many red blood cells have settled quickly, which may suggest:

• an infection
• an inflammatory illness, such as an autoimmune disease
• some types of cancer

ESR may be higher due to older age, pregnancy or anaemia. Some medicines may also affect your ESR result.

In some conditions, such as sickle cell disease, ESR levels can be very low.

It is important to talk to your doctor about your results so they can explain what they mean for you.

Pathology Tests Explained (Opens in new tab) provides information about the ESR blood test (Opens in new tab).

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.