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Definition of Macroglobulinemia
Medically reviewed by Min Clinic Staff | Updated: January 2026
Macroglobulinemia: A condition in which the blood contains high levels of large proteins. If the levels are too high the blood may become too thick or viscous and thus become too thick to flow through small blood vessels. The large protein is an antibody called macroglobulin or IgM. One type of macroglobulinemia is Waldenström's macroglobulinemia, a type of cancer.