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Immunoglobulin G (IgG) in Serum

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of Immunoglobulin G (IgG), a type of antibody found in your blood. IgG helps protect your body from infections and diseases.

Quick summary

["IgG helps fight infections and supports long-term immunity."]

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

Key facts at a glance

LOINC
27434-0
Short code
Deprecated S pneum23 IgG sp1 Ser IA-mCnc
Synonyms
Deprecated S pneum23 IgG sp1 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

What Does IgG Serve in the Body?

IgG is the most abundant antibody in your blood and plays a critical role in defending against bacteria and viruses. It can cross the placenta to provide passive immunity to a newborn, helping protect the baby from infections during early life.

Why Might Your Doctor Order This Test?

Your doctor may check IgG levels to assess immune function, diagnose conditions like immunodeficiency, evaluate responses to vaccines, or monitor diseases such as lupus or certain cancers that affect antibody production.

Common Reasons for Testing

Common reasons include identifying immune system disorders, checking vaccine effectiveness, diagnosing chronic infections, or monitoring conditions that alter antibody production.

What to Expect Before the Test

No special preparation is needed. A blood sample will be drawn from a vein, usually in your arm. You may feel a slight pinch, but it should only take a few minutes.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance of IgG Levels

Short name

IgG Level

Frequently asked questions

What Are Normal IgG Levels?
Normal IgG levels vary by age and health status. Your doctor will compare your results to your specific reference range and overall health.
How Often Should IgG Levels Be Checked?
Your doctor will determine how often you need this test based on your medical history, symptoms, and treatment plan. Regular monitoring may be necessary if you have an ongoing condition affecting immunity.
Can IgG Levels Change with Age?
Yes, IgG levels can change with age. Infants have lower IgG levels initially, which increase as they grow. In adults, levels may fluctuate due to infections, vaccinations, or certain medical conditions.
  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