Phlebotomy

Phlebotomy is the draining of blood from a vein. In pre-scientific medicine, "bloodletting" was a common, although often harmful, concept in restoring "balance" among the humors conceived by Hippocrates.

Classic bloodletting
Hippocrates, while the spiritual father of medicine and whose ethics and examining techniques remain valuable, was not a very good physiologist. He is credited with defining metabolism in terms of the "Four Humours": blood, phlegm, bile, and black bile. If they were out of balance, the patient suffered, and, by the theory of the time, an excess (usually of blood) needed to be released. Galen, one of the most famous of ancient physicians, enthusiastically endorsed bloodletting, up to and including unconsciousness.

Phlebotomy in modern medicine
In modern medicine, phlebotomy, with sterile technique, is a common procedures, although done for very different reasons in the past. It is the method by which blood is obtained from a donor to a blood bank, and is the most common means to draw blood for laboratory analysis.

While most modern phlebotomies are diagnostic, they can be therapeutic. In iron overload disorders such as hemochromatosis, frequent withdrawal of blood avoids toxic buildup.

Phlebotomy can be an emergency treatment when the heart or lungs are in fluid overload, as in heart failure or pulmonary edema. The goal is to limit the workload on the body's pumping organs. Tourniquets applied sequentially to one limb at a time also can reduce load, without actual blood loss.

Blood may be drawn well before elective surgery, to be available for autotransfusion into the patient. During cardiopulmonary bypass, blood is withdrawn during the anesthesia process, and returned to the patient at the end of surgery; this tends to reduce transfusion requirements.