Refers to a kind of protein that is carried in the liquid part of the blood (plasma). There are three classes of globulin: alpha, beta, and gamma. Each can be subdivided further; for example, there is an alpha I and an alpha II globulin. Each of the globulin proteins has an important function in the body.

Alpha and beta globulins combine loosely with other important body chemicals to carry them around in the blood. Alpha I globulin contains a fraction that binds bilirubin and another one that carries steroids and lipids. Alpha II globulin combines with free hemoglobin in the plasma. Beta globulins include some that are responsible for transporting lipids and others that bind copper and iron for transport. Prothrombin, one of the blood-clotting factors, is a beta globulin. The gamma globulins are extremely important in the body’s immune system: They are known alternatively as immunoglobulins and are subdivided into classes (IgA, IgE, igM, etc.) according to their function.

The overall pattern of alpha, beta, and gamma globulins may be measured to assess the progress of many different types of disease and treatment, since they quite commonly are affected. The specific immunoglobulins are also useful diagnostic indicators.