Immunoglobulin G (IgG) Subclass Measurement (Serum/Plasma)

What IgG Subclasses Does This Test Measure?

IgG is divided into four subclasses (IgG1, IgG2, IgG3, IgG4), each with distinct roles. IgG1 and IgG2 are most involved in fighting bacterial and viral infections, while IgG3 has a strong role in activating immune cells. IgG4 is less common and may be associated with allergic responses or autoimmune conditions. This test evaluates the concentration of these subclasses in your blood.

Why Might You Need This Test?

Doctors may order IgG subclass testing if you have recurrent infections, immune system disorders (like common variable hypogammaglobulinemia), autoimmune diseases, or if you’re receiving treatments that affect your immune response. It can also help diagnose or monitor conditions like HIV, certain cancers, or allergic reactions.

How Is This Test Performed?

A blood sample is drawn from a vein, usually in your arm. The blood is then processed to separate serum or plasma, which is sent to a lab for analysis. The lab uses immunoassay methods (such as enzyme-linked immunosorbent assay, or ELISA) to measure the precise levels of each IgG subclass.

What Do My Results Mean?

Results show the concentration of each IgG subclass in milligrams per deciliter (mg/dL) or similar units. While reference ranges vary by lab, lower-than-expected levels in certain subclasses may indicate immune dysfunction, while higher-than-expected levels might suggest conditions like allergic reactions or certain autoimmune diseases. Your doctor will interpret these results in the context of your overall health.