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Immunoglobulin G (IgG) in Serum or Plasma

Published: August 9, 2026Updated: August 17, 2026

This test measures the amount of Immunoglobulin G (IgG), a type of antibody in your blood. IgG is important for fighting infections and is the most common antibody in the body.

Quick summary

["IgG helps your immune system defend against bacteria and viruses."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
102913-1
Short code
Sheep Milk IgE RAST
Synonyms
Sheep Milk IgE RAST
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
10
Ref high
40
Critical range
— – 500 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
rast
CPT
84484
SNOMED
302774002
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 IgG Used For?

IgG levels can help doctors diagnose or monitor conditions like immune deficiencies, infections, autoimmune diseases, or certain cancers. It may also be checked if you’re planning pregnancy to assess immune function or if you have symptoms of low immunity.

How Is This Test Done?

A blood sample is taken from a vein, usually in your arm. The blood is then sent to a lab for testing. The test measures the concentration of IgG in your serum or plasma.

Why Might You Need This Test?

Your doctor may order an IgG test if you have recurring infections, fatigue, joint pain, or symptoms suggesting an immune disorder. It can also be used to check for conditions like HIV, hepatitis, or certain types of cancer.

What Do Results Mean?

Results may be compared to a reference range provided by your lab. Low IgG levels could indicate a weakened immune system, while very high levels might suggest certain immune disorders or chronic infections.

Reference range

Adult: 10-40 U/LN/A

Specimen: serum

No special preparation required. Avoid fatty meals before the test if possible.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

IgG Level

Frequently asked questions

Why do I need this test?
Your doctor may need to check your IgG levels to diagnose or monitor conditions affecting your immune system, such as infections, autoimmune diseases, or immune deficiencies.
What does a low IgG level mean?
A low IgG level may suggest a weakened immune system, which could make you more prone to infections. Your doctor may recommend additional tests or treatments to support your immune function.
How long does it take to get results?
Results are typically available within 1 to 3 business days, depending on your lab and testing process.
  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 17, 2026. · Read our editorial policy