You are in Medical Library . Why The Test Is Performed Blood is used by the body for transportation of oxygen, food, waste products, and other materials within the body. It is also used for regulation of body temperature, regulation of fluids, and acid-base equilibrium.
Plasma contains various substances dissolved in the fluid.
The cellular portion consists primarily of red blood cells, but also includes white blood cells and platelets . Because blood is used for multiple functions within the body, tests on the blood or its components may give valuable clues in the diagnosis of a multitude of medical conditions. A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding .