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Casein-Specific IgG Antibodies — Radioallergosorbent Test (RAST), Qualitative

Published: August 9, 2026Updated: August 17, 2026

A qualitative blood test that detects IgG antibodies directed against casein, a protein found in milk.

Quick summary

["A positive result shows a casein-specific IgG immune response but does not by itself confirm milk allergy."]

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

Key facts at a glance

LOINC
21146-6
Short code
Deprecated Casein IgG RAST Ql
Synonyms
Deprecated Casein IgG RAST Ql
Category
liver
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
10
Ref high
40
Critical range
— – 500 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
84484
SNOMED
302774002
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 is this test?

This test looks for IgG antibodies against casein, a milk protein. Casein-specific IgG can develop after exposure to milk or milk-containing foods.

Why might I need this test?

It may be used to evaluate a suspected immune response to milk proteins or to help interpret a suspected food-related reaction. Results must be considered alongside symptoms, diet, and other allergy testing.

How is the test performed?

A blood sample is tested using a radioallergosorbent method, which detects casein-specific IgG and reports the result as positive or negative. The laboratory may use a different but related laboratory method.

How do I prepare for the test?

No special preparation is usually required. Tell your healthcare professional if you have recently changed your diet, consumed dairy products, or are taking medicines that may affect immune test results.

Reference range

Adult: 10-40 U/LN/A

Specimen: serum

No special preparation required. Avoid fatty meals before the test if possible.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

A positive result indicates that IgG antibodies to casein are present, which may reflect milk exposure or a previous immune response. Casein-specific IgG is not a validated stand-alone test for milk allergy or food intolerance, so symptoms and medical history must guide interpretation. A negative result does not completely exclude a reaction to milk.

Short name

Casein-Specific IgG Antibodies (RAST)

Frequently asked questions

Does a positive result mean I have a milk allergy?
No. A positive casein-specific IgG result shows immune exposure or sensitization to casein but does not by itself diagnose milk allergy. Allergy evaluation generally depends on the type and timing of symptoms and, when appropriate, skin-prick or IgE testing.
Is this the same as a casein-specific IgE test?
No. This test detects IgG antibodies, while casein-specific IgE testing evaluates the type of immune response more closely associated with immediate allergic reactions. Your clinician can explain which test is appropriate for your situation.
Do I need to avoid dairy if the result is positive?
Do not start a restricted diet based only on this result. Discuss the finding with your healthcare professional, especially if you have digestive symptoms, hives, swelling, wheezing, or another possible milk reaction.
  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