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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; abnormal levels may indicate immune system issues."]

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

Key facts at a glance

LOINC
40903-7
Short code
Deprecated S pneum12 IgG Ser IA-mCnc
Synonyms
Deprecated S pneum12 IgG Ser IA-mCnc
Category
coagulation
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 to evaluate immune function, diagnose conditions like hypogammaglobulinemia, or monitor treatment responses in cases of immune-related disorders. It may also be used to assess immune responses to infections or vaccines.

What to Expect Before the Test

No special preparation is needed. You may have blood drawn from a vein in your arm. If you’re on blood thinners, inform your provider beforehand to avoid unnecessary delays or complications.

What the Results Mean

IgG subclasses are measured in mass concentration (e.g., grams per liter). While reference ranges vary by lab, lower-than-expected levels may suggest weakened immune responses, while higher-than-expected levels could indicate chronic infections or autoimmune conditions.

Common Conditions Linked to IgG Subclass Levels

Abnormal IgG subclass results can signal conditions such as primary immunodeficiency, chronic infections, or autoimmune diseases. For example, low IgG2 levels might be linked to poor vaccine responses, while elevated IgG levels could indicate long-term inflammation or immune activation.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

IgG Subclass Levels

Frequently asked questions

How long does it take to get my IgG subclass test results?
Results are typically available within 1–3 business days, depending on your lab’s processing time. Follow-up with your healthcare provider to discuss findings and next steps.
Can I eat or drink before this test?
You can eat and drink normally before the test, as it’s a blood draw with no dietary restrictions.
What if my IgG subclass levels are outside the expected range?
If your results are abnormal, your provider will review them with you to determine the cause—whether it’s an infection, immune disorder, or another factor—and guide further testing or treatment.
  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