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Serum Immunoglobulin G (IgG) Subclass 1, 2, 3, 4 Quantification

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

This test measures the levels of different subclasses of Immunoglobulin G (IgG), a key protein in your immune system. IgG helps fight infections and is divided into four subclasses (IgG1, IgG2, IgG3, IgG4), each with distinct roles.

Quick summary

Understanding your IgG subclass levels can help identify immune system strengths or weaknesses.

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

Key facts at a glance

LOINC
56548-1
Short code
U1 snRNP IgG Ser IA-aCnc
Synonyms
U1 snRNP IgG Ser IA-aCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
ia
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 Might Be Ordered

Your healthcare provider may order this test if you have symptoms like frequent infections, autoimmune conditions, or if you’re being treated for a condition that affects your immune response. It can also be used to monitor immune function in certain chronic diseases or after treatments like chemotherapy.

What to Expect Before the Test

No special preparation is needed. You’ll provide a blood sample, usually drawn from a vein in your arm. The test is quick and typically done in a lab setting. If you’re on blood thinners, let your provider know before the test.

What the Results Mean

IgG subclasses work together to support immunity, but each has a unique function. Low levels in certain subclasses might suggest immune deficiencies or certain autoimmune diseases, while high levels could be linked to conditions like chronic infections or certain cancers.

Common Conditions Monitored

This test is often used to diagnose or monitor conditions such as common variable immunodeficiency (CVID), autoimmune diseases (like rheumatoid arthritis), or to assess immune response after treatments like stem cell transplants.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

IgG subclasses play distinct roles in immunity. For example, IgG1 and IgG3 are primarily involved in neutralizing viruses and bacteria, while IgG2 helps fight bacterial infections. IgG4 is less well understood but may be linked to allergic responses. Abnormal levels can indicate immune system imbalances, which may require further evaluation or treatment to address underlying causes.

Short name

IgG Subclass Levels

Frequently asked questions

What does a low IgG subclass level mean?
Low levels of certain IgG subclasses may suggest an immune deficiency, where your body struggles to produce enough antibodies to fight infections. This could lead to frequent or severe infections, especially bacterial ones. Your provider may recommend additional tests or treatments to support your immune system.
How often should I get this test?
The frequency depends on your health condition and treatment plan. If you have a known immune disorder, your provider may recommend regular monitoring. If you’re asymptomatic, this test might not be routine unless symptoms arise or your provider suspects an issue with your immune function.
Can diet or supplements affect IgG subclass levels?
While diet and supplements can influence overall immune health, they may not directly affect IgG subclass levels. Focus on a balanced diet rich in vitamins and minerals, and discuss any supplements with your provider before starting them, as some may interact with test results or treatments.
  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