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Casein Immunoglobulin G (IgG) Quantification in Serum

Published: August 9, 2026Updated: August 15, 2026

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

Quick summary

["IgG levels help assess immune function and identify potential deficiencies or immune-related conditions."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 15, 2026Editorial policy

Key facts at a glance

LOINC
18418-4
Short code
CASEINIGA
Synonyms
Casein IgA Qn
Category
chemistry
Sample
serum
Container
Serum separator tube (SST) or red-top tube with clot activator
Units
N/A
Ref low
10
Ref high
20
Fasting
false
Population
adult
Sex
all
Age range
≥ 0 years
Method
Enzyme-Linked Immunosorbent Assay (ELISA) / Quantitative Immunoassay
CPT
83516
SNOMED
121831000221107
Specimen volume
1-2 mL of serum (minimum 0.5 mL)
Stability
Serum stable for 7 days at 2-8°C; for longer storage, freeze at -20°C or below for up to 6 months. Avoid repeated freeze-thaw cycles.
Hemolysis max
100
Lipemia max
100
Icterus max
50
TAT
24–72 hours
Order
routine

What Is Immunoglobulin G (IgG)?

IgG is the primary antibody your immune system produces to fight off infections. It’s found in high levels in the blood and plays a key role in long-term immunity. Your body produces IgG in response to bacteria, viruses, and toxins, helping to neutralize them and mark them for destruction by other immune cells.

Why Might You Need This Test?

Doctors may order this test if you have symptoms like frequent infections, slow wound healing, or if you’re at higher risk for infections due to conditions like HIV, chemotherapy, or certain autoimmune diseases. It can also help monitor immune function in newborns or individuals with immune system disorders.

How Is the Test Performed?

A small blood sample is taken from a vein in your arm. The blood is then processed to separate serum (the liquid part without clots) for testing. The IgG level is measured using an immunoassay, which detects the presence and quantity of IgG antibodies in the serum.

What Do Results Mean?

Results are compared to a reference range, which can vary slightly by lab. Low IgG levels may suggest an immune deficiency, while very high levels might indicate chronic infections, certain cancers, or autoimmune conditions. Your doctor will interpret results in the context of your overall health and symptoms.

Reference range

Reference range varies by laboratory and assay manufacturer; generally reported in units/mL (e.g., <10 U/mL considered negative, 10-20 U/mL equivocal, >20 U/mL positive). Results should be interpreted in conjunction with clinical findings and other diagnostic criteria for celiac disease.N/A

Specimen: serum

No special preparation required. Patient should be on a regular gluten-containing diet prior to testing, as antibody levels may decrease on a gluten-free diet and yield false-negative results. Fasting is not required.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: Low or High IgG Levels

Short name

IgG Serum Level

Frequently asked questions

How often will I need to retest?
Retesting frequency depends on your medical condition and doctor’s recommendations. If you have an immune deficiency or ongoing treatment (like chemotherapy), your doctor may schedule follow-up tests to monitor IgG levels over time. If you’re healthy, retesting is usually only done if symptoms or conditions change.
What are the typical reference ranges for IgG?
Reference ranges for IgG vary by lab and age. For adults, they often fall between 6.0 to 16.0 grams per deciliter (g/dL). For children, ranges differ, so your doctor will provide age-specific guidance. Your test results will be compared to your lab’s specific reference values.
Can lifestyle changes affect IgG levels?
Yes, certain lifestyle factors may influence IgG levels indirectly. A balanced diet rich in protein and vitamins (like vitamin D and zinc) supports immune function. Stress, poor sleep, and chronic illnesses can also impact immune responses, so maintaining overall health is important. Always follow your doctor’s advice regarding diet or supplements.
  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 15, 2026. · Read our editorial policy