Immunoassay for Immunoglobulin G (IgG) Subclasses (Serum)
This test measures the levels of different types of Immunoglobulin G (IgG), a key protein in your immune system, in your blood serum. IgG helps protect your body from infections and diseases.
["IgG subclasses play distinct roles in immunity and may be checked if you have suspected immune deficiencies or autoimmune conditions."]
Key facts at a glance
- LOINC
- 110046-0
- Short code
- CASIGG
- Synonyms
- Casein IgG Msmt Ser
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST) — red-top or gold-top tube; alternatively plain red-top tube with serum separation
- Units
- N/A
- Ref low
- 10
- Ref high
- 20
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- Enzyme-Linked Immunosorbent Assay (ELISA) / Quantitative IgG Immunoassay
- CPT
- 86001
- SNOMED
- 395127008
- Specimen volume
- 1-2 mL serum (minimum 0.5 mL); pediatric minimum 0.3 mL serum
- Stability
- Room temperature: 24 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C or lower): 30 days; avoid repeated freeze-thaw cycles
- Hemolysis max
- 100
- Lipemia max
- 100
- Icterus max
- 50
- TAT
- 48–168 hours
- Order
- routine
Why This Test Might Be Ordered
Your healthcare provider may recommend this test if you have symptoms like frequent infections, unusual fatigue, or if you’ve been diagnosed with an autoimmune disorder. It can also help assess immune function in conditions like lupus, rheumatoid arthritis, or certain immune system disorders.
What to Expect Before the Test
No special preparation is needed. You’ll have a small needle inserted into your arm to draw blood. If you’re on blood thinners, let your provider know before the test.
What the Results Mean
IgG is the most abundant antibody in your blood, but it’s divided into four subclasses (IgG1, IgG2, IgG3, IgG4). Abnormal levels may indicate immune system issues, such as low resistance to infections or overactive immune responses.
Common Conditions Linked to IgG Levels
Low IgG levels can weaken your immune system, increasing susceptibility to infections. High levels may be seen in autoimmune diseases or chronic inflammation. Your provider will interpret results in the context of your health history and symptoms.
Reference range
Negative: <10 U/mL; Low/Moderate Positive: 10-20 U/mL; High Positive: >20 U/mL (Reference ranges vary by laboratory and assay manufacturer)N/A
No special preparation required. Patient may continue normal diet prior to specimen collection unless otherwise directed by clinician
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
IgG subclass levels
Frequently asked questions
What does an abnormal IgG subclass result mean?
Will I need to take any medications before or after this test?
How often will I need this test?
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 15, 2026. · Read our editorial policy