Blood Test: Erythrocyte Sedimentation Rate

What Is an Erythrocyte Sedimentation Rate Test?

An erythrocyte sedimentation rate test (also called an ESR or sed rate test) measures the speed at which red blood cells fall to the bottom of an upright glass test tube. This measurement is important because when a person's blood has abnormal amounts of certain proteins in it, they cause red blood cells to clump together and sink more quickly.

Why Is It Done?

The ESR helps doctors detect inflammation or irritation in the body that may be caused by infection, some cancers, and certain autoimmune diseases such as rheumatoid arthritis, lupus, and Kawasaki disease. The ESR test alone can't be used to diagnose any specific disease, however.

Preparation

If your doctor asks you to get an ESR test, you won't need to do anything special beforehand to get ready. 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.

The Procedure

A health professional will usually draw the blood from a vein in your arm — most often on the inside of the elbow, but sometimes on the back of the hand. The technician cleans the skin surface with antiseptic and ties an elastic band (tourniquet) around the upper arm so the veins swell with blood and are easy to see.

Next, it's time for the needle. It should feel like a quick pinprick. Occasionally, it can be hard to find a vein so a nurse, doctor, or technician might need to try more than once. That's not the norm, though — most people's veins are easy to find.

It's best to try to relax and stay still during the procedure since 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 backwards, doing some breathing exercises, thinking of a place that makes you happy, or listening to music.

The technician will draw the blood so it collects in a vial or syringe. Collecting blood will only take a few minutes. Once the technician has enough blood, he or she removes the needle and covers the area with cotton or a bandage to stop the bleeding.

After the test, you may notice some bruising — that's normal and it should go away in a few days. Don't be afraid to ask the technician if you have any questions about the blood draw.

Safety

A blood test is a safe procedure and there are no real risks. Some people may feel faint or lightheaded during a blood test. And while nobody really loves needles, a few teens have a strong fear of them. If that's you, talk to your doctor since there are things that can be done to make the procedure easier for you.

Results

It usually only takes a few hours or a day or so for your doctor to get the results of an ESR test. If the test seems to show problems, your doctor may want to do other tests to find out what the cause is.

Reviewed by: Steven Dowshen, MD
Date reviewed: March 2011

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Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor.

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