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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 in your immune system. IgG subclasses help protect against bacteria, viruses, and toxins.

Quick summary

["IgG subclasses play a vital role in immune defense and can be checked if you have immune-related conditions or symptoms."]

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

Key facts at a glance

LOINC
27374-8
Short code
Deprecated S pneum12 IgG Ser-mCnc
Synonyms
Deprecated S pneum12 IgG Ser-mCnc
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 Might Be Ordered

Your healthcare provider may order this test to evaluate immune function, diagnose or monitor conditions like immunodeficiency, autoimmune diseases, or infections. It can also help assess how well your body produces antibodies in response to vaccines or illnesses.

What to Expect Before the Test

No special preparation is needed for this blood test. You may have a small needle inserted into your arm or hand to draw a blood sample. The process usually takes a few minutes, and you can resume normal activities afterward.

What the Results Mean

IgG subclasses are measured in grams per liter (g/L) or milligrams per deciliter (mg/dL). Lower than expected levels may indicate immune deficiencies, while higher levels could be associated with certain autoimmune diseases or chronic infections. Your results will be compared to standard reference ranges provided by your lab.

Common Conditions Monitored or Diagnosed

IgG subclass testing is often used to diagnose or monitor conditions such as common variable immunodeficiency (CVID), HIV/AIDS, certain autoimmune diseases (like lupus or rheumatoid arthritis), and to check immune response after vaccination.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: IgG Subclasses and Immune Function

Short name

IgG Subclass Levels

Frequently asked questions

What does it mean if my IgG subclass levels are low?
Low IgG subclass levels may suggest an underlying immune deficiency, which can increase your risk of frequent infections. Your doctor may recommend further evaluation, including additional blood tests or immune function studies, to determine the cause and guide treatment options.
Can elevated IgG subclass levels indicate a problem?
Elevated IgG subclass levels can sometimes be seen in chronic infections, autoimmune diseases, or certain types of cancer. These findings may prompt further investigation to identify the underlying cause and guide appropriate management.
Why would my doctor order IgG subclass testing?
Your doctor might order this test if you have symptoms of a weakened immune system, such as frequent infections, recurrent pneumonia, or if you’ve had a recent diagnosis of an immunodeficiency or autoimmune condition. It can also be used to monitor immune response after treatments or vaccinations.
  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