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 detect 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 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 a child 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 may also be used to follow how well treatment for inflammation or infection is working. How Should We Prepare for an ESR Test? Your child should be able to eat and drink normally unless also getting other tests that require fasting beforehand. Tell your doctor about any medicines your child takes because some drugs might affect the test results. Wearing a T-shirt or short-sleeved shirt for the test can make things easier for your child, and you also can bring along a toy or book as a distraction. 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 In babies, blood draws are sometimes done as a "heel stick collection." After cleaning the area, the health professional will prick your baby's heel with a tiny needle (or lancet) to collect a small sample of blood. Collecting a sample of blood is only temporarily uncomfortable and can feel like a quick pinprick. Can I Stay With My Child During an ESR Test? Parents usually can stay with their child during a blood test. Encourage your child to relax and stay still because tensing muscles can make it harder to draw blood. Your child might want to look away when the needle is inserted and the blood is collected. Help your child to relax by taking slow deep breaths or singing a favorite song. 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 kids might feel faint or lightheaded from the test. A few kids and teens have a strong fear of needles. If your child is 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 for your child 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. Back to Articles Related Articles Getting a Blood Test (Video) A blood test might sound scary, but it usually takes less than a minute. Watch what happens in this video for kids. Read More Blood Test (Video) These videos show what's involved in getting a blood test and what it's like to be the person taking the blood sample. Read More Lupus Lupus is known as an autoimmune disease in which a person's immune system mistakenly works against the body's own tissues. Read More Lupus Lupus is a disease that affects the immune system. Learn how lupus is treated, signs and symptoms, how to support a friend who has it, and more. Read More Kawasaki Disease Kawasaki disease is an illness that causes inflammation in blood vessels throughout the body. When symptoms are noticed early and treated, kids begin to feel better within a few days. Read More Immune System The immune system is made up of special cells, proteins, tissues, and organs that defend people against germs and microorganisms. Read More Immune System The immune system, composed of special cells, proteins, tissues, and organs that protect against germs and microorganisms, is the body's defense against disease. Read More Juvenile Idiopathic Arthritis In juvenile idiopathic arthritis (also called juvenile rheumatoid arthritis)), a person can develop swollen, warm, and painful joints. Learn more. Read More Blood Test: Erythrocyte Sedimentation Rate (ESR) This test measures the speed at which red blood cells fall to the bottom of an upright glass test tube. Find out why doctors do it and what's involved for teens. Read More Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. © 1995-2021 KidsHealth®. All rights reserved. Images provided by The Nemours Foundation, iStock, Getty Images, Veer, Shutterstock, and Clipart.com.