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, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill 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.
For infants and small 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. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
A special stain can be used to identify reticulocytes, because they contain a substance called RNA, while fully mature red blood cells do not. The number of reticulocytes in the blood indicates how quickly they are being produced and released by the bone marrow. Normally, the body will respond to bleeding or hemolytic anemia (breakdown of red blood cells) by an increased rate of red blood cell production. A lower-than-normal percentage of reticulocytes usually indicates a nutritional deficiency.
| 
