Immunoglobulin G (IgG) Subclass 3 Mass Concentration in Serum

What Does This Test Measure?

IgG3 is one of five subclasses of Immunoglobulin G (IgG), the most common antibody in your blood. This subclass plays a role in fighting bacterial infections, particularly those caused by encapsulated bacteria like *Streptococcus pneumoniae* or *Haemophilus influenzae*. While IgG3 is less abundant than other IgG subclasses, it is highly effective at activating immune responses. Your doctor may order this test if you have symptoms of immune dysfunction, recurrent infections, or certain autoimmune conditions.

Why Might You Need This Test?

A doctor may recommend measuring IgG3 levels if you have concerns about your immune system, such as frequent infections, unusual reactions to vaccines, or suspected immune deficiencies. It can also be part of monitoring for conditions like common variable immunodeficiency (CVID) or other antibody-related disorders.

What Does a Low or High Level Mean?

Low IgG3 levels may suggest an immune system that isn’t producing enough of this subclass, which could increase your risk of infections. High levels might be seen in certain autoimmune diseases or after immune stimulation (e.g., infections or vaccines). However, reference ranges vary by lab, and results are interpreted in the context of your overall health.

How Is This Test Done?

A blood sample is drawn from a vein in your arm. The blood is then processed to separate serum, where the IgG3 antibody is measured using a specialized immunoassay technique. The test is typically done in a clinical laboratory and results are reported as a mass concentration (often in grams per liter).