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Serum/plasma mass concentration of immunoglobulin G (IgG) by nephelometry

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

This test measures the amount of Immunoglobulin G (IgG), the most common type of antibody in your blood. IgG helps fight infections and is important for long-term immunity.

Quick summary

["IgG levels help assess immune function and identify potential immune deficiencies or infections."]

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

Key facts at a glance

LOINC
102961-0
Short code
M racemosus IgG RAST
Synonyms
M racemosus IgG 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 antibody produced by your immune system to protect against bacteria and viruses. It’s the most abundant antibody in your blood and plays a key role in long-term immunity. Your body makes IgG in response to infections or vaccines to help your immune system remember past illnesses and defend against future ones.

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, slow healing wounds, or unexplained fatigue. It can also be used to monitor immune responses after treatments like chemotherapy or stem cell transplants.

When Is This Test Done?

This test is typically done through a simple blood draw from a vein in your arm. The blood sample is sent to a lab where it is analyzed using nephelometry, a method that measures how much light is scattered by antibodies in your blood.

What Do My Results Mean?

Results may be compared to a reference range provided by your healthcare provider, which can vary slightly depending on the lab. Low IgG levels may suggest an immune deficiency, while very high levels could indicate conditions like multiple myeloma 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 (Serum/Plasma)

Frequently asked questions

What causes low IgG levels?
Low IgG levels can be caused by conditions that weaken the immune system, such as HIV/AIDS, certain cancers (like lymphoma or multiple myeloma), or long-term use of steroids. It can also occur in people with certain genetic disorders or those who have had a bone marrow transplant.
What causes high IgG levels?
High IgG levels may be seen in chronic infections, autoimmune diseases (like rheumatoid arthritis), or certain types of cancer, such as multiple myeloma. In some cases, it can also be a normal response to repeated infections or vaccinations.
How often should I get this test?
The frequency of IgG testing depends on your health condition and treatment plan. If you have an immune-related disorder, your doctor may recommend testing every few months or as needed to monitor changes in your levels.
  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