Skip to content

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 is the most common antibody and plays a key role in defending against infections.

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
31635-6
Short code
Deprecated S pneum 1 IgG sp1 Ser-aCnc
Synonyms
Deprecated S pneum 1 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

Why This Test Might Be Ordered

Your healthcare provider may order this test if you have symptoms like frequent infections, low immune response, or if they suspect an immune-related condition. It could also be part of a broader evaluation for autoimmune diseases or certain genetic disorders.

What to Expect Before the Test

No special preparation is needed. You may have a small needle inserted into your arm or hand to draw blood. If you’re nervous, let your provider know—they can offer comfort measures.

What the Results Mean

Results show the concentration of IgG subclasses (IgG1, IgG2, IgG3, IgG4) in your serum. Abnormal levels may indicate immune system issues, such as hypogammaglobulinemia or certain autoimmune diseases.

Common Conditions Linked to IgG Subclass Testing

Low IgG subclass levels can suggest weakened immunity, while high levels may be linked to chronic infections, certain cancers, or overactive immune responses. This test helps guide treatment plans.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

IgG subclass testing is important for diagnosing or monitoring conditions like recurrent infections, immunodeficiency, or autoimmune disorders. It helps tailor treatments to address specific immune system challenges.

Short name

IgG Subclass (Serum)

Frequently asked questions

What does a low IgG subclass level mean?
A low IgG subclass level may indicate an immune deficiency, where your body struggles to produce enough antibodies to fight infections. This could be due to genetic factors, certain medications, or chronic illnesses.
How long does it take to get results?
Results are typically available within 1 to 3 business days, depending on your lab’s processing time. Your healthcare provider will discuss them with you during your follow-up visit.
Can diet or supplements affect IgG subclass levels?
Dietary changes alone won’t significantly alter IgG subclass levels, but certain medications (like steroids) or chronic illnesses may influence them. Always follow your provider’s advice regarding supplements or treatments.
  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