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Immunoglobulin G (IgG) Subclass Measurement (Serum)

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

This test measures the levels of different subclasses of Immunoglobulin G (IgG), a key antibody protein in your blood that helps fight infections and diseases.

Quick summary

["Understanding your IgG subclass levels can 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
22549-0
Short code
Deprecated S pneum3 IgG Ser-aCnc
Synonyms
Deprecated S pneum3 IgG Ser-aCnc
Category
coagulation
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
82784
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why This Test Is Done

Doctors may order this test to evaluate immune function, diagnose conditions like hypogammaglobulinemia (low antibody levels), or monitor treatment responses in patients with chronic illnesses or immune disorders.

What to Expect Before the Test

No special preparation is needed. You’ll provide a blood sample, typically drawn from a vein in your arm. The test is quick and usually done in a lab setting.

What the Results Mean

IgG is divided into four subclasses (IgG1, IgG2, IgG3, IgG4). Abnormal levels in any subclass may indicate immune system issues, such as reduced ability to fight infections or autoimmune diseases.

Common Conditions Affecting IgG Levels

Low IgG subclass levels can be linked to conditions like common variable immunodeficiency (CVID), HIV/AIDS, or chronic illnesses like lupus or rheumatoid arthritis. High levels may rarely suggest immune system overactivity or certain infections.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

IgG Subclass Levels

Frequently asked questions

What causes IgG subclass levels to change?
IgG subclass levels can fluctuate due to infections, chronic illnesses, immune system disorders, aging, or certain medications. If you suspect an underlying condition, discuss your symptoms and medical history with your healthcare provider.
How often should I get this test?
Your doctor will determine the frequency based on your health needs. Tests may be repeated if symptoms persist, treatment is underway, or if monitoring immune function is part of your ongoing care plan.
Can diet or lifestyle affect IgG levels?
While diet and lifestyle can influence overall immune health, IgG subclass levels are primarily determined by immune system function. Focus on a balanced diet, hydration, and avoiding excessive stress to support general immune health.
  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