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Immunoassay for Immunoglobulin G (IgG) Subclass Quantification (Serum/Plasma)

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 immune system. IgG subclasses help protect against infections and play roles in immune responses.

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
9874-9
Short code
Rhythm Seg Imp EKG
Synonyms
Rhythm Seg Imp EKG
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
ekg
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 recommend this test if you have symptoms like frequent infections, autoimmune conditions, or if they suspect an immune disorder. It can also be used to monitor treatment responses in conditions affecting the immune system.

What to Expect Before the Test

No special preparation is needed for this test. You may have a blood draw, where a small amount of blood is taken from a vein in your arm. If you’re on blood thinners, let your provider know before the test.

What the Test Results Mean

IgG subclasses are measured in grams per liter (g/L). Abnormal levels may indicate immune system issues, such as low or high subclass production, which can affect your body’s ability to fight infections or respond to vaccines.

Common Conditions Linked to IgG Subclass Levels

Low IgG subclass levels may be linked to conditions like common variable immunodeficiency (CVID), where the immune system doesn’t produce enough antibodies. High levels might suggest chronic infections or certain autoimmune diseases.

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 change due to infections, autoimmune diseases, certain medications, or immune system disorders. Age, genetics, and overall health also play a role. If you’ve had recent illnesses or treatments, this could affect your results.
How often should I get this test?
Your provider will determine how often you need this test based on your health condition, symptoms, and treatment plan. Some people may need it yearly or more frequently if they have ongoing immune-related issues.
Can I eat or drink before this test?
You can eat and drink normally before this test unless instructed otherwise. Blood tests typically don’t require fasting unless specified for other tests.
  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