A macroglobulin is a plasma globulin of high molecular weight.

Elevated levels of macroglobulins (macroglobulinemia

Macroglobulinemia

Macroglobulinemia is the presence of increased levels of macroglobulins in the circulating blood.A plasma cell dyscrasia resembling leukemia with cells of lymphocytic, plasmacytic, or intermediate morphology, which secrete an immunoglobulin M monoclonal component. There is diffuse infiltration of...

) may cause manifestations of excess blood viscosity (as is the case for IgM

IGM

IGM as an acronym or abbreviation can refer to:* Immunoglobulin M , the primary antibody against A and B antigens on red blood cells* International Grandmaster, a chess ranking* intergalactic medium* Intragroup medium - see: Intracluster medium...

 antibodies in Waldenström macroglobulinemia

Waldenström macroglobulinemia

Waldenström's macroglobulinemia is cancer involving a subtype of white blood cells called lymphocytes. The main attributing antibody is Immunoglobulin M . WM is an "indolent lymphoma,"...

) and/or precipitate within blood vessels when temperature drops (as in cryoglobulinaemia).

Other macroglobulins include alpha-2 macroglobulin, which is elevated in nephrotic syndrome

Nephrotic syndrome

Nephrotic syndrome is a nonspecific disorder in which the kidneys are damaged, causing them to leak large amounts of protein from the blood into the urine....

, diabetes, severe burns, and other conditions, while a deficiency is associated with chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease , also known as chronic obstructive lung disease , chronic obstructive airway disease , chronic airflow limitation and chronic obstructive respiratory disease , is the co-occurrence of chronic bronchitis and emphysema, a pair of commonly co-existing diseases...

.