Immunoglobulin G (IgG) Subclass Measurement (Serum)

Why This Test Is Done

Doctors may order this test if you have symptoms like frequent infections, recurrent sinus or ear infections, or if you’ve been diagnosed with a condition like common variable immunodeficiency (CVID). It can also help evaluate immune responses to vaccines or monitor immune-related diseases.

What to Expect Before the Test

No special preparation is needed. You’ll have a small needle inserted into your arm or hand to draw a blood sample. The process is quick and usually painless. If you’re nervous, let your healthcare provider know so they can offer comfort measures.

What the Results Mean

IgG subclasses are measured in grams per deciliter (g/dL). While reference ranges vary slightly by lab, IgG1 is typically the most abundant (about 70% of total IgG), followed by IgG2, IgG3, and IgG4. Abnormal levels in any subclass may indicate immune dysfunction or other health concerns.

Possible Findings and Next Steps

If your IgG subclass levels are low in certain subclasses, your doctor may recommend further testing, such as antibody response to vaccines, or treatments like immunoglobulin therapy. If levels are high, they may investigate underlying conditions like autoimmune diseases or chronic infections.