Immunoglobulin G (IgG) Subclass Measurement (Serum)

This test measures the four main subclasses of immunoglobulin G in your blood: IgG1, IgG2, IgG3, and IgG4. Each subclass plays a slightly different role in defending the body against infections, so measuring them individually helps your doctor understand how well your immune system is functioning.

IgG is divided into four subclasses (IgG1, IgG2, IgG3, IgG4), each with distinct roles in immunity. This test typically evaluates the concentration of one or more of these subclasses, though exact subclasses may vary by lab. IgG1 and IgG2 are most commonly assessed together.

Your doctor may order this test if you have frequent or unusual infections, such as repeated sinus or lung infections, or if routine immunoglobulin results suggest a possible immune problem. It can also help monitor a known immune deficiency or check how well antibody replacement therapy is working over time.

Doctors may order this test to diagnose or monitor conditions like immune deficiencies, autoimmune diseases, infections, or certain cancers. It can also help evaluate how well your immune system is responding to treatments.

A blood sample is drawn from a vein in your arm, usually at a laboratory or clinic. No special preparation is needed for most people, but tell your healthcare provider about any medications or supplements you take, since some can affect IgG levels. Follow any specific instructions your provider gives you before the draw.

A blood sample is drawn from a vein, usually in your arm. The blood is processed to separate serum (the liquid part after clotting), which is then analyzed for IgG subclass levels.

Before the test, your healthcare provider will explain the reason for testing and answer any questions you have. You can usually eat and drink normally beforehand unless told otherwise. When you arrive, a technician will clean the puncture site, and you may feel a brief pinch as the needle is placed. The collection takes only a few minutes.

No special preparation is needed, but inform your healthcare provider about any medications or recent illnesses. Avoid strenuous activity 24 hours before the test if instructed.