What is the ESR test?

The erythrocyte sedimentation rate (ESR) blood test is done to check for diseases causing inflammation in your body. It measures how many of your red blood cells (erythrocytes) fall to the bottom of a test tube in 1 hour.

The ESR is also called the sedimentation rate, or sed rate.

Why is this test done?

The ESR test may help diagnose and treat a medical problem you are having. It does not diagnose a specific problem but it can help your healthcare provider know what other tests you might need. It’s also a way to see how well treatment for a disease is working.

How do I prepare for this test?

• You may need to avoid taking certain medicines before the test because they might affect the test result. Make sure your healthcare provider knows about any medicines, herbs, or supplements that you are taking. Ask your provider before stopping any of your regular medicines.
• Talk to your healthcare provider if you have any questions about the test.

How is the test done?

Having this test will take just a few minutes. A small amount of blood is taken from a vein in your arm with a needle. The blood is collected in tubes and sent to a lab.

Ask your healthcare provider when and how you will get the result of your test.

What do the test results mean?

When there is inflammation in the body, the red blood cells stick together more than normal and fall to the bottom of the test tube more quickly. This means that more of them fall to the bottom of the test tube in 1 hour than when there is no inflammation. Your ESR may be higher than normal if you have a disease or problem that is causing inflammation, such as:

• Arthritis
• Autoimmune disease (a disease that causes your body to mistakenly attack your own tissues, like lupus)
• Infection
• Cancer

The ESR is also higher during pregnancy or if you have kidney or thyroid disease. Your healthcare provider will use the result of your ESR test, the history of your illness, your physical exam, and any other tests you may have had to arrive at a diagnosis.

Some diseases cause inflammation but do not raise the ESR, so a normal result does not always mean that you do not have a medical problem.

A low ESR is usually not a problem. However, your ESR may be lower than normal if you have:

• A disease or condition that increases red blood cell production
• A disease or condition that increases white blood cell production
• Sickle cell anemia (abnormal red blood cells)

If you are being treated for an inflammatory disease, an ESR that is going down is a good sign that your body is responding to the treatment.

What if my test result is not normal?

Test results are only one part of a larger picture that takes into account your medical history, physical exam, and current health. Sometimes a test needs to be repeated to check the first result. Talk to your healthcare provider about the results and ask questions, such as:

• If you need more tests
• What kind of treatment you might need
• What lifestyle, diet, or other changes you might need to make