A serum globulin (invariably an immunoglobulin) that precipitates at low temperatures: Cryoglobulin is an abnormal blood protein that has the unusual properties of precipitating from the blood serum when it is chilled (hence the "cryo-") and redissolving when it is rewarmed. Cryoglobulins are gamma globulins with a molecular weight of approximately 200,000.

Cryoglobulins can cause problems by causing the blood to be abnormally "thick" which increases the risk of blood clots forming in the brain (stroke), eyes, and heart.

Cryoglobulins are also associated with inflammation of blood vessels (vasculitis) which increases the risk of blockage of arteries.

Cryoglobulins are a key part of a condition called essential mixed cryoglobulinemia. Cryoglobulins can also accompany diseases such as multiple myeloma, dermatomyositis, and lymphoma.

Sometimes small amounts of cryoglobulin are discovered by accident in the laboratory in a serum sample from someone with no apparent symptoms.