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Serum Immunoglobulin G (IgG) Concentration

Published: August 9, 2026Updated: August 17, 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 critical role in long-term immunity and are often checked if you have recurring infections or immune system concerns."]

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

Key facts at a glance

LOINC
102381-1
Short code
Horse Serum Prot IgE RAST
Synonyms
Horse Serum Prot 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

Why This Test Is Done

Doctors may order an IgG test to evaluate your immune system function. Possible reasons include diagnosing or monitoring conditions like immunodeficiency, autoimmune diseases, or infections. It may also be used to check for antibody responses after vaccination or to monitor treatment progress in certain disorders.

What to Expect Before the Test

No special preparation is needed. You may have a small needle inserted into a vein in your arm to draw blood. The process usually takes a few minutes. If you’re nervous, let your healthcare provider know—they can help make it more comfortable.

What the Test Results Mean

IgG levels can vary based on health, age, and other factors. While specific ranges aren’t provided here, low IgG levels might suggest weakened immunity, while very high levels could indicate overactive immune responses or certain medical conditions. Always discuss results with your doctor.

Common Conditions Monitored

IgG tests help diagnose or track conditions like common variable immunodeficiency (CVID), HIV/AIDS, certain autoimmune diseases, or infections. They may also assess antibody production after vaccination or treatment for conditions like cancer.

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

What might cause abnormal IgG levels?
Abnormally low IgG levels may indicate an immune system disorder, chronic infections, or malabsorption issues. High IgG levels can sometimes signal autoimmune diseases, chronic inflammation, or certain cancers. Always consult your healthcare provider for interpretation.
How often should I get this test?
Your doctor will determine how often you need this test based on your health needs. Some people may need it yearly or more frequently if they have ongoing conditions like immunodeficiency or autoimmune diseases.
Can diet or supplements affect IgG levels?
Dietary changes alone won’t significantly alter IgG levels, but certain supplements or medications might. If you’re taking supplements or changing your diet, discuss it with your doctor to ensure it doesn’t interfere with test results or treatment.
  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