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Serum Immunoglobulin G (IgG) Concentration

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

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

Quick summary

["IgG helps protect your body against diseases and infections by identifying and neutralizing harmful substances."]

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

Key facts at a glance

LOINC
31657-0
Short code
Deprecated S pneum9 IgG sp2 Ser-aCnc
Synonyms
Deprecated S pneum9 IgG sp2 Ser-aCnc
Category
coagulation
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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

Why This Test Might Be Ordered

Your healthcare provider may order this test to check for low or high levels of IgG, which can occur due to immune system conditions, chronic illnesses, or certain medications. It may also be used to monitor treatment progress in conditions like HIV, autoimmune diseases, or after organ transplants.

What to Expect Before the Test

No special preparation is needed for this blood test. You may have a small needle inserted into your arm to draw blood, and you’ll rest for a few minutes afterward. If you’re on blood thinners, let your provider know before the test.

What the Results Mean

Results are compared to a general reference range, but individual ranges can vary. Low IgG levels may indicate weakened immunity, while very high levels could suggest overactive immune responses or certain diseases. Your provider will discuss the results with you in detail.

Common Reasons for Testing

IgG testing is often done to diagnose or monitor conditions like recurrent infections, immunodeficiency disorders, or immune system disorders. It may also be used in research or to assess immune response to vaccines.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

IgG Level

Frequently asked questions

What does IgG stand for?
Immunoglobulin G is the most common type of antibody in your blood. It plays a key role in defending against bacteria and viruses, as well as helping your body remember past infections for faster protection in the future.
Can IgG levels change with age?
Yes, IgG levels can vary with age. Infants have lower IgG levels initially, which rise as they develop immunity. In adults, levels may fluctuate due to illness, medications, or immune system conditions.
How long does it take to get results?
Results are typically available within 1 to 3 business days, depending on your lab and healthcare provider’s process. Your provider will contact you once they have the results.
  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