Allergen-Specific IgG4 Antibodies, Qualitative — Radioallergosorbent Test (Deprecated)
A qualitative blood test that may detect IgG4 antibodies against selected allergens. It is marked as deprecated and should not be used alone to diagnose allergy.
["This test may show prior exposure to selected allergens, but a positive result does not by itself confirm an allergy."]
Key facts at a glance
- LOINC
- 26418-4
- Short code
- Deprecated C herbarum IgG4 RAST Ql
- Synonyms
- Deprecated C herbarum 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 laboratory test uses a radioallergosorbent test, or RAST, method to look for allergen-specific IgG4 antibodies in a blood sample. IgG4 is one type of immunoglobulin, a protein made by the immune system.
Why might I need this test?
It may be included in the evaluation of a suspected food-related reaction or to assess immune response to selected allergens. Because food-specific IgG4 testing is now considered deprecated and can occur without clinical allergy, results must be interpreted with symptoms, exposure history, and other medical findings.
How is the test performed?
A blood sample is tested in the laboratory using the RAST method to determine whether allergen-specific IgG4 antibodies are present. The result is reported as positive or negative for the allergens evaluated.
How do I prepare for the test?
No special preparation is usually required, and fasting is generally unnecessary. Follow any instructions from your healthcare professional, particularly if this test is being ordered as part of a broader allergy evaluation.
Reference range
Adult: 10-40 U/LN/A
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 IgG4 antibodies to the tested allergen are present, which may reflect prior exposure or immune sensitization. It does not establish that the substance is causing symptoms, and a negative result does not exclude an allergy. Your clinician should interpret the result alongside your history, physical examination, and any allergy testing they consider appropriate.
Short name
Allergen-Specific IgG4 (RAST)
Frequently asked questions
Does a positive result mean I am allergic?
Why is this test marked as deprecated?
Do I need to avoid the suspected allergen before the test?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
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.
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