American Board of Internal Medicine (ABIM) Certification Practice Exam

IgG4-related disease is associated with elevated levels of what substance in the serum?

1. IgE

2. Immunoglobulin M

3. Immunoglobulin G4

4. Immunoglobulin A

The correct answer is: Immunoglobulin G4

In IgG4-related disease, there is a notable increase in the levels of Immunoglobulin G4 (IgG4) in the serum. This condition is characterized by a systemic immune-mediated process that often leads to the formation of tissue inflammation and fibrosis in various organs. Elevated IgG4 levels serve as a significant biomarker for diagnosing and monitoring the disease. The presence of high IgG4 levels is thought to reflect an underlying pathological process where IgG4-producing plasma cells proliferate, leading to the clinical manifestations of the disease such as mass lesions in organs like the pancreas, salivary glands, and kidneys. The measurement of serum IgG4 is critical in distinguishing IgG4-related disease from other conditions that might present similarly, such as autoimmune pancreatitis or malignancies. In contrast, other immunoglobulin types such as IgE, Immunoglobulin M (IgM), and Immunoglobulin A (IgA) do not show the same significant association with IgG4-related disease. While they are important in various other clinical contexts, their levels are not typically used as markers for the diagnosis or management of IgG4-related conditions. Therefore, the correct answer highlights the characteristic serum finding in this specific disease process.