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Blood Test: Erythrocyte Sedimentation Rate (ESR)

What Is a Blood Test?

A blood test is when a sample of blood is taken from the body to be tested in a lab. Doctors order blood tests to check things such as the levels of glucose, hemoglobin, or white blood cells. This can help them look for problems like a disease or medical condition. Sometimes, blood tests can help them see how well an organ (such as the liver or kidneys) is working.

What Is an ESR Test?

An ESR test measures how quickly red blood cells settle to the bottle of a test tube. Inflammation (swelling and irritation) or infection can lead to extra proteins in the blood, which can make the red blood cells settle faster. When this happens, the ESR is higher.

Why Are ESR Tests Done?

An ESR test may be done if someone has signs of inflammation or infection. ESR tests are used to follow activity levels of conditions such as inflammatory bowel disease (IBD), arthritis, and lupus. ESR tests are also used to follow how well treatment for inflammation or infection is working.

How Should I Prepare for an ESR Test?

You should be able to eat and drink normally unless also getting other tests that require fasting beforehand. Tell your doctor about any medicines you take because some drugs might affect the test results.

It can help to wear a T shirt or other short-sleeve top on the day of the test to make things faster and easier for the technician who will be drawing the blood.

How Is an ESR Test Done?

Most blood tests take a small amount of blood from a vein. To do that, a health professional will:

  • clean the skin 
  • put an elastic band (tourniquet) above the area to get the veins to swell with blood
  • insert a needle into a vein (usually in the arm inside of the elbow or on the back of the hand)
  • pull the blood sample into a vial or syringe
  • take off the elastic band and remove the needle from the vein

It's best to try to relax and stay still during the procedure because tensing muscles can make it harder and more painful to draw blood. And if you don't want to watch the needle being inserted or see the blood collecting, you don't have to. Look the other way and maybe relax by focusing on saying the alphabet backward, doing some breathing exercises, thinking of a place that makes you happy, or listening to your favorite music.

How Long Does an ESR Test Take?

Most blood tests take just a few minutes. Occasionally, it can be hard to find a vein, so the health professional may need to try more than once.

What Happens After an ESR Test?

The health professional will remove the elastic band and the needle and cover the area with cotton or a bandage to stop the bleeding. Afterward, there may be some mild bruising, which should go away in a few days.

When Are ESR Test Results Ready?

Blood samples are processed by a machine, and it may take a few hours to a day for the results to be available. If the test results show signs of a problem, the doctor might order other tests to figure out what the problem is and how to treat it.

Are There Any Risks From ESR Tests?

An ESR test is a safe procedure with minimal risks. Some people might feel faint or lightheaded from the test. A few teens have a strong fear of needles. If you're anxious, talk with the doctor before the test about ways to make the procedure easier.

A small bruise or mild soreness around the blood test site is common and can last for a few days. Get medical care if the discomfort gets worse or lasts longer.

If you have questions about the ESR test, speak with your doctor or the health professional doing the blood draw.

Reviewed by: Larissa Hirsch, MD
Date reviewed: January 2018

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