Immunoglobulin G (IgG) Subclass Measurement (Serum)
This test measures the levels of different subclasses of Immunoglobulin G (IgG), a key antibody protein in your immune system. IgG subclasses help protect against infections and regulate immune responses.
["Understanding your IgG subclass levels can help identify immune system function or deficiencies."]
Key facts at a glance
- LOINC
- 16638-9
- Short code
- C immitis IgG CSF-aCnc
- Synonyms
- C immitis IgG CSF-aCnc
- Category
- chemistry
- Sample
- csf
- Container
- Sterile tube
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 82784
- Specimen volume
- 1-2 mL
- Stability
- Immediate analysis required, Refrigerated: 1h
- Hemolysis max
- 200
- TAT
- 4–24 hours
- Order
- routine
Why This Test Might Be Ordered
Your healthcare provider may recommend this test if you have symptoms like frequent infections, autoimmune conditions, or if you’re being evaluated for immune-related disorders. It could also be part of a broader evaluation for conditions affecting antibody production, such as certain immune deficiencies or chronic illnesses.
What to Expect Before the Test
No special preparation is needed for this blood test. You may be asked to fast for 8–12 hours before your blood draw if your provider specifies it, but this is not always required for IgG subclass testing alone.
How the Test Works
A small amount of blood is drawn from a vein in your arm. The blood sample is then analyzed in a lab to measure the concentration of each IgG subclass (IgG1, IgG2, IgG3, IgG4). The results help determine if any subclass is significantly lower or higher than expected.
What the Results Mean
Results are typically expressed as mass concentration (e.g., grams per liter). While reference ranges vary slightly by lab, lower-than-expected levels of certain subclasses may suggest immune system issues, while higher levels could indicate chronic inflammation or other conditions.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
IgG subclass testing is important for diagnosing or monitoring conditions like common variable immunodeficiency (CVID), HIV/AIDS, or other immune disorders. For example, low IgG2 levels may be linked to recurrent sinus or respiratory infections, while abnormal IgG4 levels could indicate autoimmune diseases or certain cancers. Your provider will interpret results in the context of your symptoms and medical history.
Short name
IgG Subclass Levels
Frequently asked questions
What causes IgG subclass levels to change?
How often should I get this test?
Can lifestyle changes affect IgG subclass levels?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy