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Serum IgG Immunoglobulin G (Mass Concentration)

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of Immunoglobulin G (IgG) in your blood serum. IgG is the most common type of antibody in your body and helps fight infections.

Quick summary

["IgG helps protect you from infections and long-term immune responses."]

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

Key facts at a glance

LOINC
17650-3
Short code
S pneum IgG sp1 Ser IA-aCnc
Synonyms
S pneum IgG sp1 Ser IA-aCnc
Category
coagulation
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
ia
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 Measure?

IgG is the primary antibody your immune system produces to defend against bacteria, viruses, and toxins. It circulates in your bloodstream and provides long-lasting protection. This test helps assess your overall immune function, especially after vaccination or infection.

Why Might You Need This Test?

Your doctor may order this 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 vaccines or treatments like chemotherapy.

How Is the Test Performed?

A blood sample is taken from a vein, usually in your arm. The blood is then sent to a lab where it is processed to separate serum (the liquid part without clots). The lab measures the concentration of IgG using a specialized immunoassay method.

What Are Possible Results?

Results are typically reported as a mass concentration (e.g., grams per liter). While reference ranges vary by lab, lower than expected levels may suggest immune deficiencies, while higher levels could indicate chronic infections, autoimmune diseases, or certain medical conditions.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

IgG Level

Frequently asked questions

What Does a Low IgG Level Mean?
Low IgG levels may indicate a primary immune deficiency, where your body doesn’t produce enough antibodies to fight infections effectively. This can lead to recurrent or severe infections, especially in children or adults with underlying health issues.
What Does a High IgG Level Mean?
High IgG levels can result from chronic infections, autoimmune diseases (like rheumatoid arthritis), or certain cancers. In some cases, it may also be a normal response to repeated exposure to an antigen, such as in long-term infections or allergies.
How Often Should I Get This Test?
Your doctor will determine the frequency based on your health needs. For example, people with known immune deficiencies may need monitoring more often, while others may only need it if symptoms arise or as part of routine check-ups.
  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