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Serum IgG Substance Concentration (Immunoglobulin G)

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

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

Quick summary

["IgG supports long-term immunity and helps fight infections."]

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

Key facts at a glance

LOINC
22562-3
Short code
S pneum IgG sp1 Ser-aCnc
Synonyms
S pneum IgG sp1 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

What Does IgG Measure?

IgG is the primary antibody produced by your immune system in response to infections, vaccines, and other immune challenges. It circulates in your bloodstream and provides broad protection against pathogens like bacteria and viruses. Levels of IgG can vary depending on your health status, immune response, and exposure to infections.

Why Might Your Doctor Order This Test?

Your doctor may order an IgG test to assess your immune system’s ability to fight infections, evaluate the effectiveness of vaccines, or diagnose conditions like immunodeficiency disorders, chronic infections, or certain autoimmune diseases. It can also help monitor treatment responses in patients with weakened immune systems.

Common Reasons for Testing

Common reasons include recurrent infections, suspected immunodeficiency, monitoring immune response after vaccination, or investigating symptoms like frequent colds, slow wound healing, or chronic fatigue that may indicate an underlying immune issue.

What to Expect Before the Test

No special preparation is usually needed for this blood test. You may be asked to fast for 8–12 hours before the test if your lab requires it, but this is not always the case for IgG testing. A healthcare provider will draw blood from a vein in your arm.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

IgG Level

Frequently asked questions

What Are IgG Levels Used For?
IgG levels help determine if your immune system is functioning properly. Low IgG levels may indicate a condition like common variable immunodeficiency (CVID), where the immune system doesn’t produce enough antibodies. High IgG levels can sometimes signal chronic infections, autoimmune diseases, or other health concerns that need further evaluation.
How Do IgG Levels Change Over Time?
IgG levels can fluctuate due to infections, vaccinations, aging, or certain medical treatments. For example, vaccinations can temporarily boost IgG levels, while chronic illnesses may lead to sustained changes. Your doctor will interpret results in the context of your overall health and medical history.
Can Diet or Lifestyle Affect IgG Levels?
Diet and lifestyle factors like nutrition, stress, and exposure to infections can indirectly influence immune function, but they do not directly alter IgG levels. Maintaining a balanced diet and managing stress can support overall immune health, though IgG testing itself is not affected by these factors.
  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