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 a Blood Culture? A blood culture is a test that looks for germs (such as bacteria or fungi) in the blood. If germs are found, the test also can help doctors know which medicines will work best to treat the infection. Why Are Blood Cultures Done? A blood culture is done when a child has signs of an infection that might be caused by bacteria or fungi. It also might be done if a child has an infection in one part of the body that may have spread into the blood. How Should We Prepare for a Blood Culture? 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 a Blood Culture 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 Collecting a sample of blood is only temporarily uncomfortable and can feel like a quick pinprick. Can I Stay With My Child During a Blood Culture? 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 a Blood Culture 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 a Blood Culture? 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 Blood Culture Results Ready? Blood samples are processed by a machine, and it may take a few days for the results to be available. If the results show signs of a problem, the doctor might order other tests to help identify it and decide how to treat it. Are There Any Risks From Blood Cultures? A blood culture 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 blood culture, speak with your doctor or the health professional doing the blood draw. Back to Articles Related Articles Blood Test: Basic Metabolic Panel A basic metabolic panel (BMP) is a group of blood tests that provide doctors with clues about how the body is working. Find out why doctors do this and what's involved for teens. 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