Venesection is the generic term for a procedure that involves the cutting of a vein in any way, but it most commonly refers to the drawing of blood from a vein. Venous blood is usually taken from the median cubital vein, which is located on the arm, opposite the elbow. Blood donation is also usually done out of this vein, but blood drawn for testing, which is the main purpose of venesection, is normally taken in quantities of about 0.17 to 0.84 fluid ounces (5 to 25 ml). The procedure is also known as phlebotomy and venipuncture.
The vein on the inside of the elbow is the preferred vein for drawing blood for a number of reasons. First, it is close to the skin, so using a needle to access it is quick and causes a minimum of trauma and bruising. This vein is also in a place which lacks an abundance of nerve endings. In other words, while having blood drawn from the arm causes some degree of discomfort to almost everyone, there are many places where it would be much more painful. Many types of medical professionals are trained to know how to draw blood from this site.
In most developed countries such as the USA, the UK, and Australia, the procedure is performed with an evacuated tube system. Typically, the needle is inserted into the patient's vein, and a hub on the needle allows a tube to be connected to it. The tubes, from which most of the air has been evacuated, are made of glass or plastic. Thanks to the design of the hub, multiple tubes can be placed on the hub, one after the other, allowing for several samples of blood to be drawn for testing at one time, if needed. The hub also prevents blood from draining out of the needle when there is not yet a tube attached.
Certain diseases can call for treatments that involve this procedire, including hemochromatosis and polycythemia. The former is characterized by an overabundance of iron in the blood, and is easily treated by venesection, which in this case amounts to bloodletting, to reduce the blood's iron content. Venesection at weekly intervals is usually the recommended treatment. Polycythemia is a somewhat similar condition in which there are too many red blood cells produced in the body. This accumulation can be due to a pathology of the bone marrow, low oxygen levels, or even simple dehydration. The drawing off of red blood cells through venesection is an effective treatment for this problem.