An erythrocyte sedimentation rate test, also called an ESR or sed rate test, measures the speed at which red blood cells settle 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, which results in a high ESR value.
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 juvenile idiopathic arthritis, lupus, and Kawasaki disease. The ESR alone can't be used to diagnose any one specific disease, however.
No special preparations are needed for this test. On the day of the test, it may help to have your child wear a T-shirt or short-sleeved shirt to allow easier access for the technician who will be drawing the blood.
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 A needle is inserted into a vein (usually in the arm inside of the elbow or on the back of the hand) and blood is withdrawn and collected in a vial or syringe.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.
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.
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. You also can talk to the technician before the procedure.