Macroglobulin
![IgM, pictured, is an example of a macroglobulin. Another example is alpha-2 macroglobulin.](/Images/godic/202501/25/IgM_scheme.svg0931.png")
A macroglobulin is a plasma globulin of high molecular weight.
Elevated levels of macroglobulins (macroglobulinemia) may cause manifestations of excess blood viscosity (as is the case for IgM antibodies in Waldenström macroglobulinemia) and/or precipitate within blood vessels when temperature drops (as in cryoglobulinaemia).