Blood sampling. Gloved hands placing a syringe in a vein in the arm in order to take a sample of blood. The process of piercing a vein with a needle is called venepuncture. Blood samples are taken to check on blood composition and quality. Most blood tests require venous blood, which is usually obtained, as here, from a vein at the bend of the elbow. A tourniquet (white) is placed around the upper arm causing the veins to swell and making them easy to locate. Rubber gloves help to maintain a sterile environment.