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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 antibodies play a key role in long-term immunity."]

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

Key facts at a glance

LOINC
40904-5
Short code
Deprecated S pneum12 IgG sp1 Ser IA-mCnc
Synonyms
Deprecated S pneum12 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 Is Immunoglobulin G (IgG)?

IgG is the most common type of antibody in your blood. It’s produced by your immune system to fight off infections, such as bacteria and viruses. IgG antibodies can also help protect you from diseases that you’ve already had, like measles or chickenpox, by providing long-term immunity.

Why Might You Need This Test?

Doctors may order an IgG test to check for low or high levels, which can indicate conditions like immune deficiencies, certain infections, or autoimmune diseases. It may also be used to monitor treatment responses in conditions affecting the immune system.

When Might You Get This Test?

You might have this test if you have symptoms of a weakened immune system, such as frequent infections, unusual bruising, or unexplained weight loss. It could also be part of a routine checkup or before certain treatments that affect immunity.

What Does the Test Involve?

A blood sample is taken from a vein in your arm. The blood is then sent to a lab where it is analyzed to measure the amount of IgG antibodies present.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: IgG Levels and Health

Short name

IgG Level

Frequently asked questions

Why is IgG important in diagnosing or managing health conditions?
IgG levels can help diagnose or monitor conditions like common variable immunodeficiency (CVID), HIV/AIDS, or certain autoimmune diseases. Low IgG levels may suggest an immune system that isn’t working as well as it should, while very high levels could indicate chronic infections or certain cancers.
How do IgG levels change over time with treatments?
If you’re receiving treatments like immunoglobulin therapy or medications to boost immunity, your IgG levels may change. Your doctor will track these levels to adjust treatment plans as needed.
What are some common reasons doctors check IgG levels?
Doctors may check IgG levels to evaluate immune function, especially in people with frequent infections, chronic illnesses, or those receiving immunosuppressive 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