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

Published: August 9, 2026Updated: August 16, 2026

This test measures the concentration of specific subclasses of Immunoglobulin G (IgG), a type of antibody in your blood. IgG is the most abundant antibody and plays a key role in defending against infections.

Quick summary

["IgG subclasses help identify immune system function and potential deficiencies."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
42511-6
Short code
IgD CSF-mCnc
Synonyms
IgD CSF-mCnc
Category
chemistry
Sample
csf
Container
Sterile tube
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
1-2 mL
Stability
Immediate analysis required, Refrigerated: 1h
Hemolysis max
200
TAT
4–24 hours
Order
routine

Why This Test Is Done

Your healthcare provider may order this test to evaluate immune function, diagnose conditions like hypogammaglobulinemia (low antibody levels), or assess responses to treatments for autoimmune diseases or infections. It can also help identify why certain infections are recurring or persistent.

What to Expect Before the Test

No special preparation is needed. You may have a blood draw from a vein in your arm. If you’re on blood thinners, inform your provider beforehand to avoid excessive bleeding.

What the Test Results Mean

Results show the concentration of IgG subclasses (IgG1, IgG2, IgG3, IgG4) in your blood. Abnormal levels may indicate immune system issues, such as low resistance to infections or autoimmune disorders. Your provider will interpret results in the context of your overall health.

Common Conditions Linked to IgG Subclass Testing

Conditions like chronic infections, recurrent sinus or ear infections, or autoimmune diseases (e.g., lupus, rheumatoid arthritis) may prompt this test. It’s also used in monitoring immune responses to vaccines or treatments for immune deficiencies.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

IgG subclass levels

Frequently asked questions

What does a low IgG subclass mean?
A low IgG subclass may indicate an immune system that struggles to produce enough antibodies, increasing your risk of frequent or severe infections. This could be due to a genetic immune deficiency, certain medications, or chronic illnesses. Your provider will work with you to determine the cause and recommend appropriate interventions, such as antibody replacement therapy or lifestyle adjustments.
What if my IgG subclass levels are normal?
Normal IgG subclass levels generally mean your immune system is functioning well to fight infections. However, your provider may still recommend follow-up testing if you have recurring infections, symptoms of an autoimmune condition, or other health concerns. They may also monitor these levels over time to ensure your immune response remains stable.
Can IgG subclass testing be done at home?
No, IgG subclass testing requires a blood sample collected in a clinical setting by a healthcare professional. Home testing kits for antibodies are not typically used for this specific subclass measurement. Always follow your provider’s instructions for any blood tests.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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