Skip to content

Immunoglobulin G (IgG) in Serum

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

This test measures the amount of Immunoglobulin G (IgG), a key protein in your immune system that helps fight infections and diseases.

Quick summary

["IgG helps protect your body from harmful invaders like bacteria and viruses."]

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

Key facts at a glance

LOINC
47345-4
Short code
Deprecated S pneum43 IgG 2:1 Ser-Rto
Synonyms
Deprecated S pneum43 IgG 2:1 Ser-Rto
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

What Does IgG Measure?

IgG is the most abundant antibody in your blood and plays a critical role in long-term immunity. It’s produced by your immune system in response to infections and helps remember past illnesses to provide faster protection if you encounter the same pathogen again.

Why Might You Need This Test?

Doctors may order an IgG test to check for immune system function, diagnose conditions like immunodeficiency, evaluate responses to vaccines, or monitor chronic diseases such as lupus or rheumatoid arthritis.

Common Reasons for Testing

Common reasons include assessing immune health, diagnosing or managing immune-related disorders, or evaluating how well vaccines are working in people with weakened immune systems.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for 8–12 hours before the blood draw if your doctor specifies it. Bring your medical records or a list of medications you’re taking.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

IgG levels can be low in people with immune deficiencies, such as HIV/AIDS, certain genetic disorders, or autoimmune diseases. High levels may indicate chronic infections, long-term exposure to toxins, or certain cancers like multiple myeloma.

Short name

IgG Level

Frequently asked questions

How long does it take to get results?
Results are typically available within 1–3 business days, depending on your lab’s processing time. Follow up with your healthcare provider to discuss the meaning of your results.
What does a low IgG level mean?
A low IgG level may suggest an underlying immune disorder that could increase your risk of infections. Your doctor will work with you to determine the best next steps, which may include further testing or treatment adjustments.
Can diet affect IgG test results?
Diet generally does not directly affect IgG levels, but certain foods or supplements (like high-protein diets) might influence overall health that indirectly impacts immune function. Always follow your doctor’s instructions for test preparation.
  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