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Immunoglobulin G (IgG) Subclass Measurement (Serum)

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

This test measures the levels of specific subclasses of Immunoglobulin G (IgG), a type of antibody in your blood. IgG is the most common antibody and plays a key role in fighting 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
25276-7
Short code
Deprecated S pneum9 IgG 2:1 Ser-Rto
Synonyms
Deprecated S pneum9 IgG 2:1 Ser-Rto
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

What IgG Subclasses Are Measured?

IgG is divided into four subclasses (IgG1, IgG2, IgG3, IgG4), each with distinct roles in immunity. This test typically evaluates the concentration of these subclasses in your serum to assess immune response variations.

Why Might This Test Be Ordered?

Doctors may order IgG subclass testing if you have recurrent infections, immune system disorders (like common variable hypogammaglobulinemia), or conditions affecting antibody production, such as HIV or certain autoimmune diseases.

How Is the Test Performed?

A blood sample is drawn from a vein in your arm. The serum (liquid part of blood without clotting factors) is then analyzed using an immunoassay method to measure IgG subclass concentrations.

What Do Results Mean?

Results show the relative amounts of each IgG subclass. Abnormal levels may indicate immune system dysfunction, such as low IgG subclasses (hypogammaglobulinemia) or high levels in certain autoimmune conditions.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

IgG Subclass Levels

Frequently asked questions

IgG subclass testing helps diagnose and monitor conditions like recurrent infections, immunodeficiency diseases, or autoimmune disorders by identifying specific antibody deficiencies or imbalances.
This test is no longer actively used in routine clinical practice due to its complexity and less common need compared to total IgG levels.
What does a low or high IgG subclass mean?
Low levels of certain IgG subclasses may suggest an immune deficiency that could increase susceptibility to infections. High levels may be associated with certain autoimmune conditions or chronic inflammation, but interpretation depends on clinical context.
How often should I get this test?
This test is rarely performed today. If ordered, it’s usually for specific diagnostic purposes, such as evaluating immune function in patients with suspected immunodeficiency or autoimmune diseases. Follow your healthcare provider’s guidance.
  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