Phlebotomy is the act of drawing or removing blood from the circulatory system through a cut (incision) or puncture in order to obtain a sample for analysis and diagnosis. Phlebotomy is also done as part of the patient's treatmentfor certain blood disorders.

Phlebotomy is part of treatment (therapeutic phlebotomy) for several diseasessuch as polycythemia vera, a condition that causes an elevated red blood cell volume. Phlebotomy is also prescribed for patients with disorders that increase the amount of iron in their blood to dangerous levels, such as hepatitisB, and hepatitis C. Patients with pulmonary edema (fluid in the lungs) may undergo phlebotomy procedures to decrease their total blood volume. Phlebotomyis also used to remove blood from the body during blood donation and for analysis of the substances contained within it. Patients who are anemic or havea history of cardiovascular disease may not be good candidates for phlebotomy.

Phlebotomy, which is also known as venesection, is performed by a nurse or atechnician known as a phlebotomist. Blood is usually taken from a vein on theback of the hand or inside of 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, slowing the blood flow in the arm and making the veins more visible. The patient is asked to make a fist, and the 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 The appropriate amount of blood is drawn and the needle is withdrawn from the vein.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 pulseand 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 thesurface 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 beingconducted. Therapeutic phlebotomy removes a larger amount of blood than donation and blood analysis require.

Patients having their blood drawn for analysis may be asked to discontinue medications or to avoid food (to fast) for a period of time before the blood test. Patients donating blood will be asked for a brief medical history, have their blood pressure taken, and have their hematocrit checked with a finger stick test prior to donation.

After blood is drawn and the needle is removed, pressure is placed on the puncture site with a cotton ball to stop bleeding, and a bandage is applied. Itis not uncommon for a patient to feel dizzy or nauseated during or after phlebotomy. The patient may be encouraged to rest for a short period once the procedure is completed. Patients are also instructed to drink plenty of fluids and eat regularly over the next 24 hours to replace lost blood volume. Patients who experience swelling of the puncture site or continued bleeding after phlebotomy should get medical help at once.

Most patients will have a small bruise or mild soreness at the puncture sitefor several days. Therapeutic phlebotomy may cause thrombocytosis (an increase in the number of blood platelets) and chronic iron deficiency (anemia) in some patients. As with any invasive procedure, infection is also a risk. Thisrisk can be minimized by the use of prepackaged sterilized equipment and careful attention to proper technique.

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