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Immunoglobulin G (IgG) by nephelometry (plasma/serum)

Published: August 9, 2026Updated: August 17, 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 helps fight infections and supports long-term immunity by recognizing and neutralizing harmful substances."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
102694-7
Short code
BLGIgG
Synonyms
B-Lactoglob IgG RAST
Category
chemistry
Sample
serum
Container
Red-top serum collection tube or serum separator tube (SST)
Units
N/A
Ref low
0.35
Ref high
0.7
Critical range
— – 500 N/A
Fasting
false
Population
adult
Sex
all
Age range
0–99 years
Method
Radioallergosorbent test (RAST) - Solid-phase immunoassay detecting specific IgG antibodies against beta-lactoglobulin in serum
CPT
86001
SNOMED
395790001
Specimen volume
1.0 mL serum minimum; 2.0 mL preferred for repeat testing
Stability
Serum stable at room temperature for 8 hours, refrigerated (2-8°C) for 7 days, frozen (-20°C) for up to 30 days. Avoid repeated freeze-thaw cycles.
Hemolysis max
100
Lipemia max
150
Icterus max
50
TAT
24–72 hours
Order
routine

What Is Immunoglobulin G (IgG)?

IgG is the most common type of antibody in your blood. Antibodies are proteins that help your immune system recognize and fight off germs like bacteria and viruses. IgG is particularly important because it can cross the placenta to protect a developing baby during pregnancy and provides long-lasting immunity after an infection has cleared.

Why Might You Need This Test?

Your doctor may order an IgG test to check for low or high levels, which can indicate conditions like immune deficiencies, infections, or certain autoimmune diseases. It may also be used in monitoring treatment responses or evaluating immune function in people with chronic illnesses.

Common Reasons for Testing

Common reasons include diagnosing or monitoring immune system disorders, assessing immune response after vaccination, evaluating chronic infections, or checking for conditions like HIV, hepatitis, or other infections where IgG levels may be abnormal.

How Is the Test Done?

A blood sample is drawn from a vein in your arm. The blood is then processed to separate the plasma or serum, which is tested for IgG levels using a specialized lab technique called nephelometry. This method measures how much light is scattered by the antibodies in the sample.

Reference range

Negative: <0.35 kU/L; Equivocal: 0.35-0.70 kU/L; Positive: >0.70 kU/L. Results reported as presence/absence of detectable beta-lactoglobulin-specific IgG antibodies.N/A

Specimen: serum

No fasting required. Patient should inform the ordering physician about current medications, particularly antihistamines or corticosteroids, which may affect immune response interpretation. Avoid recent allergen exposure documentation when possible.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance of IgG Levels

Short name

IgG Level

Frequently asked questions

What does an abnormal IgG level mean?
Low IgG levels may suggest an immune deficiency, such as common variable immunodeficiency (CVID), or conditions that impair immune function, like severe malnutrition or certain cancers. High IgG levels can sometimes indicate chronic infections, autoimmune diseases, or other health conditions that trigger an overactive immune response.
How often should I get this test?
Your doctor will determine the frequency of testing based on your medical history, symptoms, and specific needs. Regular monitoring may be recommended if you have a chronic condition, are undergoing treatment for an immune-related disorder, or if you’re at higher risk for infections.
Can diet or lifestyle affect IgG levels?
While diet and lifestyle can influence overall immune health, IgG levels are primarily determined by your immune system’s response to infections, vaccines, and other factors. However, maintaining a balanced diet rich in vitamins and minerals can support general immune function.
  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 17, 2026. · Read our editorial policy