Last updated: 11/24/2009

Phlebotomy is performed by a nurse or a technician known as a phlebotomist. Blood is usually taken from a vein on the back of the hand or just below the elbow. Some blood tests, however, may require blood from an artery. The skin over the area is wiped...

with an antiseptic, and an elastic band is tied around the arm. The band acts as a tourniquet, retaining blood within the arm and making the veins more visible. The phlebotomy technician feels the veins in order to select an appropriate one. When a vein is selected, the technician inserts a needle into the vein and releases the elastic band. The appropriate amount of blood is drawn and the needle is withdrawn from the vein. The patient's pulse and blood pressure may be monitored during the procedure.

For some tests requiring very small amounts of blood for analysis, the technician uses a finger stick. A lance, or small needle, makes a small cut in the surface of the fingertip, and a small amount of blood is collected in a narrow glass tube. The fingertip may be squeezed to get additional blood to surface.

The amount of blood drawn depends on the purpose of the phlebotomy. Blood donors usually contribute a unit of blood (500 mL) in a session. The volume of blood needed for laboratory analysis varies widely with the type of test being conducted. Typically one or several small (5–10 mL) tubes are drawn. Therapeutic phlebotomy removes a larger amount of blood than donation and blood analysis require. Phlebotomy for treatment of hemochromatosis typically involves removing a unit of blood—250 mg of iron—once a week. Phlebotomy sessions are required until iron levels return to a consistently normal level, which may take several months to several years. Phlebotomy for polycythemia vera removes enough blood to keep the patient's hematocrit (proportion of red blood cells) below 45%. The frequency and duration of sessions depends on the patient's individual needs.