What It Is

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 abnormal proteins are present in the blood, typically due to inflammation or infection, they cause red blood cells to clump together and sink more quickly.

Why It's Done

The ESR is useful in detecting inflammation 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 alone can't be used to diagnose any one specific disease, however.

Preparation

No special preparations are needed for this test. Having your child wear a short-sleeve shirt on the day of the test can make things easier for your child and the technician who will be drawing the blood.

The Procedure

A health professional will usually draw the blood from a vein. For an infant, the blood may be obtained by puncturing the heel with a small needle (lancet). If the blood is being drawn from a vein, the skin surface is cleaned with antiseptic, and an elastic band (tourniquet) is placed around the upper arm to apply pressure and cause the veins to swell with blood. A needle is inserted into a vein (usually in the arm inside of the elbow or on the back of the hand) and blood is withdrawn and collected in a vial or syringe.

After the procedure, the elastic band is removed. Once the blood has been collected, the needle is removed and the area is covered with cotton or a bandage to stop the bleeding. Collecting blood for this test will only take a few minutes.

What to Expect

Either method (heel or vein withdrawal) of collecting a sample of blood is only temporarily uncomfortable and can feel like a quick pinprick. Afterward, there may be some mild bruising, which should go away in a few days.

Getting the Results

ESR test results are usually available within a few hours or the next day. If results seem to suggest inflammation, the doctor may order further tests to determine the specific cause of the problem.

Risks

The ESR test is considered a safe procedure. However, as with many medical tests, some problems can occur with having blood drawn, such as:

• fainting or feeling lightheaded
• hematoma (blood accumulating under the skin causing a lump or bruise)
• pain associated with multiple punctures to locate a vein

Helping Your Child

Having a blood test is relatively painless. Still, many kids are afraid of needles. Explaining the test in terms your child can understand might help ease some of the fear.

Allow your child to ask the technician any questions he or she might have. Tell your child to try to relax and stay still during the procedure, as tensing muscles and moving can make it harder and more painful to draw blood. It also may help if your child looks away when the needle is being inserted into the skin.

If You Have Questions

If you have questions about the ESR test, speak with your doctor.

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