Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to apply pressure and cause the vein to swell with blood. A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding. In infants or young children: The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any bleeding. An antibody defends the body against bacteria, viruses, fungus, or other foreign bodies (antigens). Microorganism can stimulate the body to produce these antibodies during active infection. Antibody production increases during the course of infection. In the first stages of an illness, little antibody may be detected. For this reason, serology tests (tests performed on serum, the fluid portion of blood that contains antibodies) are often repeated 10 days - 2 weeks or more after the initial sample. In the laboratory, the antibodies react with antigens in specific ways that can be used to confirm the identity of a microorganism.
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