How is IgG4 RD diagnosed?
Elevated serum IgG4 antibodies are only seen in ∼66% of patients and may be seen in other disease states. Thus, elevated serum IgG4 should not be considered sufficient for diagnosis. Rather, diagnosis should be made primarily based on pathologic features: the presence of dense lymphoplasmacytic infiltrates in a “storiform fibrosis” pattern with associated obliterative phlebitis and eosinophilia as well as having >40% of total plasma cells and >10 cells/high power field being IgG4-positive plasma cells on biopsy of involved tissue. In this setting, a total serum IgG4 concentration of >135 mg/dL helps confirm the diagnosis.
