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Casein-Specific IgG4 Antibody — Radioallergosorbent Test, Qualitative (Deprecated)

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

A legacy blood test that detects IgG4 antibodies directed against casein, a protein found in milk.

Quick summary

["A detectable result shows an immune response to casein but does not by itself diagnose milk allergy."]

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

Key facts at a glance

LOINC
26416-8
Short code
Deprecated Casein IgG4 RAST Ql
Synonyms
Deprecated Casein IgG4 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 qualitative test measures casein-specific IgG4 antibodies using a radioallergosorbent test (RAST) method. Casein is a major protein found in cow's milk. This is a legacy test that is no longer commonly used.

Why might I need this test?

It may have been ordered to evaluate an immune response to milk proteins. Results are most useful when reviewed with symptoms, exposure history, and other allergy testing.

How is the test performed?

A blood sample is tested for antibodies that bind to casein. Because this is a qualitative assay, the report generally indicates whether casein-specific IgG4 was detected rather than providing a measured concentration.

How do I prepare for the test?

No special preparation is usually required for a routine antibody blood test. Follow any instructions from the ordering clinician or laboratory, and do not stop medications without medical advice.

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.

◆Associated findings1

Short name

Casein IgG4 (RAST)

Frequently asked questions

Does a positive casein IgG4 result mean I am allergic to milk?
No. IgG4 is generally associated with exposure or immune tolerance and is not the same type of antibody used to diagnose an immediate milk allergy. Clinical symptoms and other appropriate tests are needed for interpretation.
What symptoms can be related to milk exposure?
Some people develop hives, swelling, wheezing, vomiting, abdominal pain, or diarrhea after consuming milk. The type and timing of symptoms can help clinicians distinguish possible allergic reactions from other conditions.
Why is this test described as deprecated?
This legacy RAST assay is no longer commonly used or may be unavailable at many laboratories. Ask the ordering clinician whether a currently available test is more appropriate for the clinical question.
  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