Blood serves a vital set of physiological functions in the body. It is a unique tissue and the composition of this circulating body fluid is an important indicator of cellular ion and metabolic status. Blood can be withdrawn from the body and the different components present in the blood can be separated and used in therapy.

The discoveries of blood groups by Landsteiner in 1900 and the nontoxic anticoagulant sodium citrate by Hustin in 1945 opened the way for rapid advances.