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Immunoglobulin G (IgG) Subclass Measurement (Serum/Plasma)

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 subclasses help protect against bacteria, viruses, and toxins.

Quick summary

["IgG subclasses play a vital role in immune defense and can be important for diagnosing or monitoring certain conditions."]

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

Key facts at a glance

LOINC
40968-0
Short code
Deprecated S pneum43 IgG Ser-mCnc
Synonyms
Deprecated S pneum43 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 recommend this test if you have symptoms of weakened immunity, such as frequent infections, or if you’re being treated for conditions like lupus, rheumatoid arthritis, or other autoimmune diseases. It may also be used to monitor immune responses after vaccination or following certain treatments.

What to Expect Before the Test

No special preparation is usually needed. You may fast for 8–12 hours before the test if instructed, but this is not always required for IgG subclass testing. Bring any medications you’re currently taking to your appointment.

How the Test Is Performed

A blood sample is drawn from a vein, usually in your arm, by a healthcare professional. The blood is then processed to separate serum or plasma for analysis.

What the Results Mean

IgG subclass levels can vary based on your health, age, and other factors. Your results will be compared to reference ranges provided by your lab and discussed with your doctor to determine if further action is needed.

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 be checked?
IgG subclass testing is often done to evaluate immune function, diagnose or monitor autoimmune diseases, assess immune responses to treatments (like chemotherapy), or investigate recurrent infections.
How long does it take to get results?
Results are typically available within 1–3 business days, depending on your lab’s processing time. Your doctor will contact you once they are ready for review.
Can lifestyle changes affect IgG subclass levels?
While diet and overall health can influence immune function, IgG subclass levels are primarily measured in blood and are less directly affected by lifestyle changes than other biomarkers. Your doctor may recommend adjustments if underlying health conditions are present.
  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