What is the purpose of this test?
Order this Immunoglobulin G, Subclass 4 Blood Test, which detects levels of IgG4 in the blood to screen for a deficiency or excess. The most prevalent immunoglobulin in human blood is IgG. It is the second most abundant protein in circulation and provides long-term protection against infectious agents through its protective antibodies. IgG consists of four different subclasses known as IgG1, IgG2, IgG3, and IgG4. A subclass deficiency occurs when one or more of these subclasses are consistently low, but the total IgG level remains normal.
Certain conditions may be linked to abnormal levels of one or more IgG subclasses. For example:
- IgG1: IgG1 deficiencies are associated with EBV infections.
- IgG2: IgG2 deficiencies are related to sino-respiratory infections and infections with encapsulated bacteria.
- IgG3: IgG3 deficiencies are associated with sinusitis and otitis media.
- IgG4: IgG4 deficiencies are associated with allergies, ataxia telangiectasia, and sino-respiratory infections.
When should I order an Immunoglobulin G, Subclass 4 Blood Test?
Individuals may order this test if they have experienced symptoms related to an IgG4 deficiency or excess. Common signs or symptoms of these conditions include:
- Recurring respiratory tract infections (sinus, lungs)
- Digestive system infections (stomach, intestines)
- Chronic diarrhea
