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Immunoassay for Human 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 levels can indicate immune system health and response to infections or treatments."]

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

Key facts at a glance

LOINC
108999-4
Short code
Hu2 IgG Msmt Ser
Synonyms
Hu2 IgG Msmt Ser
Category
chemistry
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 IgG Serve in the Body?

IgG is the most abundant antibody in your blood and plays a crucial role in long-term immunity. It helps fight off bacteria and viruses by marking them for destruction by immune cells. Low levels may suggest immune deficiencies or chronic infections, while high levels could indicate overactive immune responses or certain medical conditions.

When Might You Need This Test?

Your doctor may order this test if you have symptoms of a weakened immune system, such as frequent infections, unexplained fatigue, or if you’re being treated for conditions like lupus, rheumatoid arthritis, or certain cancers. It’s also used to monitor immune responses in people with HIV/AIDS or after receiving certain vaccines.

What to Expect Before the Test

No special preparation is needed for this blood test. You may have a small needle inserted into your arm to draw a blood sample. The process usually takes a few minutes, and you can resume normal activities afterward.

What the Results Mean

Results are compared to a general reference range, though individual ranges can vary. Low IgG levels may require further investigation into immune function, while very high levels could warrant evaluation for conditions like monoclonal gammopathy or autoimmune diseases.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

IgG Serum Level

Frequently asked questions

Why did my doctor ask for this test?
Your doctor may have recommended this test to assess your immune system’s ability to fight infections, monitor a known condition, or evaluate your response to treatment. Common reasons include frequent illnesses, immune deficiencies, or ongoing medical concerns.
What does a low IgG level mean?
A low IgG level may suggest a weakened immune system, which could be due to conditions like HIV/AIDS, certain cancers, or autoimmune diseases. It might also occur in people with malabsorption issues or those on certain medications. Your doctor will guide you on next steps based on your overall health.
Can IgG levels change with age?
Yes, IgG levels can vary with age. Infants and young children have lower IgG levels compared to adults, as their immune systems are still developing. In older adults, IgG levels may also fluctuate due to factors like chronic illness or reduced immune function. Your doctor will consider your age and health when interpreting results.
  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