Serum IgG Substance Concentration (Total Immunoglobulin G)
This test measures the amount of Immunoglobulin G (IgG), the most common type of antibody in your blood. IgG helps protect your body from infections and diseases.
["IgG levels help identify immune system function and potential deficiencies."]
Key facts at a glance
- LOINC
- 102339-9
- Short code
- Johnson grass IgE RAST
- Synonyms
- Johnson grass 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 Immunoglobulin G (IgG)?
IgG is a type of protein (antibody) produced by your immune system to fight infections like bacteria and viruses. It’s the most abundant antibody in your blood and plays a key role in long-term immunity. Your body produces IgG throughout your life to remember past infections and protect against future ones.
Why Might You Need This Test?
Doctors may order an IgG test if you have symptoms of a weakened immune system, such as frequent infections, slow wound healing, or unexplained fatigue. It can also be used to diagnose conditions like immunodeficiency disorders, certain autoimmune diseases, or to monitor treatment responses in people with chronic illnesses.
When Might You Get This Test?
You might receive this test if you have symptoms of an immune issue, if you’re being treated for a condition that affects antibodies, or if your doctor wants to check how well your immune system is working after a transplant or other medical treatment.
What Does a Low or High IgG Level Mean?
Low IgG levels may suggest an immune deficiency or problems absorbing nutrients (like celiac disease). High IgG levels can sometimes indicate chronic infections, autoimmune diseases, or allergic reactions. However, results alone don’t always point to a specific condition—your doctor will consider your symptoms and medical history.
Reference range
Adult: 10-40 U/LN/A
No special preparation required. Avoid fatty meals before the test if possible.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
IgG levels can indicate whether your immune system is functioning normally or if there are underlying issues like chronic infections, autoimmune diseases, or conditions affecting antibody production. Low levels may require further testing to rule out immunodeficiency or malabsorption issues, while high levels may need investigation into chronic inflammation or immune responses.
Short name
IgG Level
Frequently asked questions
What Are Common Reasons for Testing IgG?
Does diet or lifestyle affect IgG levels?
Can IgG levels change over time?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
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.
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