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Serum Immunoglobulin G (IgG) Level

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

This test measures the amount of Immunoglobulin G (IgG) in your blood, a key protein that helps protect your body from infections.

Quick summary

["IgG helps fight bacteria and viruses, and low levels may indicate immune system issues."]

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

Key facts at a glance

LOINC
16635-5
Short code
C immitis IgA Ser IA-aCnc
Synonyms
C immitis IgA Ser IA-aCnc
Category
chemistry
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 Measure?

IgG is the most abundant antibody in your blood, playing a central role in long-term immunity. It’s produced by your immune system in response to infections and vaccines. Measuring IgG helps doctors assess your immune response and identify conditions like immunodeficiency or chronic infections.

Why Might You Need This Test?

Your doctor may order an IgG test if you have symptoms of a weakened immune system (such as frequent infections), if you’re recovering from an illness, or if you’re being evaluated for conditions like HIV, lupus, or certain autoimmune diseases. It can also be used to monitor immune responses after vaccination.

How Is the Test Performed?

A blood sample is drawn from a vein in your arm. The blood is then sent to a lab, where it’s analyzed to measure the concentration of IgG antibodies. The result is typically reported as a mass concentration (in grams per liter or milligrams per deciliter).

What Are Possible Results?

Results are interpreted in the context of your overall health and medical history. Low IgG levels may suggest an immune deficiency, while very high levels could indicate chronic infections, certain cancers, or other conditions. Your doctor will discuss these findings with you.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

IgG levels are crucial for diagnosing and managing immune-related conditions. Low IgG can signal a deficiency in your body’s ability to fight infections, while elevated levels may point to chronic inflammation, autoimmune disorders, or other systemic issues. Regular monitoring of IgG can help track immune function, especially in patients with chronic illnesses or those undergoing treatments that affect immunity.

Short name

IgG Level

Frequently asked questions

What causes low IgG levels?
Low IgG levels can be caused by primary immune deficiencies (such as selective IgA deficiency or common variable immunodeficiency), chronic illnesses (like HIV/AIDS or certain cancers), long-term use of certain medications, or conditions that affect the liver or kidneys. It may also occur in newborns or premature infants due to incomplete immune development.
What causes high IgG levels?
High IgG levels are often seen in chronic infections (like tuberculosis or hepatitis), autoimmune diseases (such as rheumatoid arthritis or lupus), certain cancers (like multiple myeloma), or long-term inflammatory conditions. In some cases, high IgG may be a normal response to repeated infections or vaccinations.
How often should I get this test?
The frequency of IgG testing depends on your medical condition. If you have an immune-related disorder, your doctor may recommend regular monitoring. Otherwise, this test is usually only ordered when symptoms or concerns suggest it’s needed, such as after vaccination or during an infection.
  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