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

Why This Test Might Be Ordered

Your healthcare provider may recommend this test if you have conditions like chronic infections, autoimmune diseases (such as lupus or rheumatoid arthritis), or if you’re receiving treatments that affect your immune response. It may also be used to monitor immune function in people with weakened immune systems, such as those with HIV or undergoing chemotherapy.

What to Expect Before the Test

No special preparation is typically needed. You may be asked to fast for 8–12 hours before the test if serum is required, but plasma can often be collected without fasting. Bring any medications or supplements you’re taking to discuss with your provider.

How the Test Works

Blood is drawn from a vein in your arm, and the sample is tested using an immunoassay method to measure the concentration of IgG subclasses (IgG1, IgG2, IgG3, IgG4). The results help identify imbalances in these subclasses that could indicate immune dysfunction.

What the Results Mean

Results show the concentration of each IgG subclass in your blood. While reference ranges vary by lab, low or high levels of specific subclasses may signal underlying health concerns, such as reduced immune response or overactive immune reactions.