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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 subclasses help protect your body against infections and play a role in immune responses.

Quick summary

["Understanding your IgG subclass levels can help identify immune system function or deficiencies."]

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

Key facts at a glance

LOINC
31656-2
Short code
Deprecated S pneum9 IgG sp1 Ser-aCnc
Synonyms
Deprecated S pneum9 IgG sp1 Ser-aCnc
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 Does This Test Measure?

IgG antibodies are divided into four subclasses (IgG1, IgG2, IgG3, IgG4), each with distinct roles in immunity. This test evaluates the concentration of one or more of these subclasses in your serum. Variations in subclass levels may indicate immune system disorders, infections, or other health conditions.

Why Might You Need This Test?

Your healthcare provider may order this test if you have symptoms of immune dysfunction, such as frequent infections, autoimmune diseases, or if you’re being evaluated for conditions like hypogammaglobulinemia or certain immune deficiencies.

What to Expect Before the Test

No special preparation is usually needed. You’ll have a small needle inserted into your arm or vein to draw blood. The process takes about 5 minutes, and you can resume normal activities afterward.

What Are the Possible Results?

Results will show the concentration of IgG subclasses in your blood. While reference ranges vary by lab, abnormal levels (either too high or too low) may suggest underlying health concerns that need further investigation.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

IgG Subclass Levels

Frequently asked questions

How long will it take to get my results?
Results are typically available within 1 to 3 business days, depending on your lab’s processing schedule. Your healthcare provider will contact you with the final report.
Can I fast before this test?
No fasting is required for this blood test. However, inform your healthcare provider about any medications or supplements you’re taking, as they may affect results.
What if my IgG subclass levels are abnormal?
If your results are outside the expected range, your doctor may recommend additional tests or treatments to address potential immune system issues. Follow-up may include further bloodwork, lifestyle adjustments, or referral to a specialist.
  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