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Serum or Plasma Mass Concentration of Immunoglobulin G (IgG) Substance Content

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

This test measures the amount of Immunoglobulin G (IgG), a key protein in your immune system, found in your blood.

Quick summary

["IgG helps protect your body from infections and is essential for long-term immunity."]

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

Key facts at a glance

LOINC
35555-2
Short code
S rostrata IgG-mCnc
Synonyms
S rostrata IgG-mCnc
Category
chemistry
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 check your IgG level to evaluate your immune system function, diagnose conditions like immunodeficiency, or monitor treatment responses for diseases such as HIV, lupus, or certain cancers. It can also be used to assess how well vaccines are working or to check for antibody deficiencies.

What to Expect Before the Test

No special preparation is usually needed. You may have a small needle inserted into a vein (typically in your arm) to draw blood. If you’re taking blood from your arm, you might feel a slight pinch or sting. If you’re concerned about needles, let your healthcare provider know.

What Happens During the Test

Blood is collected in a tube and sent to a lab for analysis. The lab measures the concentration of IgG in your serum or plasma using a specialized immunoassay or nephelometry method.

What the Results Mean

Results are compared to standard reference ranges to determine if your IgG level is within normal limits, low, or high. Low IgG levels may indicate a weakened immune system, while high levels could suggest certain autoimmune conditions or infections.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

IgG Level

Frequently asked questions

What causes IgG levels to be low?
Low IgG levels can be caused by conditions like primary immunodeficiency, certain autoimmune diseases, chronic liver disease, malnutrition, or treatments that weaken the immune system, such as chemotherapy or long-term steroids.
What causes IgG levels to be high?
High IgG levels may result from chronic infections, autoimmune diseases (like lupus or rheumatoid arthritis), certain cancers, or long-term exposure to allergens. Sometimes, it can also be a normal response to repeated infections or vaccinations.
How often should I get this test?
The frequency of IgG testing depends on your medical condition and treatment plan. Your healthcare provider will determine how often you need this test based on your individual needs, such as monitoring immune function, vaccine response, or managing a chronic illness.
  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