Immunoglobulin G (IgG4), Subclass 4 details

IgG4 is one of four subclasses of IgG antibodies, normally present in only small amounts. Elevated IgG4 is associated with IgG4-related disease, a rare but increasingly recognized inflammatory condition in which IgG4-producing cells and elevated IgG4 antibodies cause tissue swelling and scarring in one or multiple organs — commonly the pancreas, bile ducts, salivary glands, or kidneys, among others. It's typically tested when this condition is suspected based on characteristic imaging findings or symptoms, and elevated levels support, but don't alone confirm, the diagnosis.