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Serum Immunoglobulin G (IgG) Level

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 important for long-term immunity.

Quick summary

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

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

Key facts at a glance

LOINC
86051-0
Short code
S pneum Da 20A IgG 2:1 Ser-Rto
Synonyms
S pneum Da 20A 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 Serve in Your Body?

IgG is the most abundant antibody in your blood and plays a critical role in defending against bacteria and viruses. It can cross the placenta to provide passive immunity to newborns and is involved in immune memory, helping your body respond faster to repeated infections.

When 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 wound healing, or unexplained fatigue. It’s also used to monitor immune responses in conditions like HIV, autoimmune diseases, or after certain treatments like chemotherapy.

Preparation for the Test

No special preparation is usually needed for this blood test. You may be asked to fast for 8–12 hours before the draw, but this depends on your doctor’s instructions. Bring any medications or supplements you’re taking, as they could affect results.

What to Expect During the Test

A healthcare professional will insert a small needle into your arm to draw a blood sample. The process is quick and typically causes minimal discomfort. You may feel a slight pinch, but most people tolerate it well. The blood sample is then sent to a lab for analysis.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

IgG Level

Frequently asked questions

Why might my IgG levels be checked regularly?
If you have a chronic illness like HIV, lupus, or have undergone treatments like chemotherapy, your doctor may monitor your IgG levels to track how your immune system is responding to treatment or managing your condition.
What could affect my IgG test results?
Several factors can influence IgG levels, including medications (like steroids), infections, pregnancy, or certain medical conditions. If you’re taking medications, have recently had an infection, or have a condition that affects your immune system, let your doctor know before the test.
Can IgG levels change over time?
Yes, IgG levels can fluctuate due to aging, immune responses to infections, or medical treatments. Regular monitoring may be needed if you have an ongoing health condition that affects your immune system, such as an autoimmune disease or immunodeficiency.
  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