A plasma globulin with high molecular weight such as IgM secreted in excess in small cell lymphoma.

A macroglobulin is a plasma globulin of high molecular weight. Elevated levels of macroglobulins (macroglobulinemia) is seen in diseases such as Waldenström macroglobulinemia. Other macroglobulins include alpha-2 macroglobulin, which is elevated in nephrotic syndrome, diabetes, severe burns, and other conditions, while a deficiency is associated with chronic obstructive pulmonary disease.