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Radioallergosorbent Test (RAST) for Allergen-Specific IgE, Qualitative — Deprecated

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

A historical blood test used to detect IgE antibodies to specific allergens, helping evaluate possible allergic sensitization.

Quick summary

["This deprecated test can show whether your immune system reacts to particular allergens, but results must be interpreted with your symptoms."]

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

Key facts at a glance

LOINC
21485-8
Short code
Deprecated Radish IgG RAST Ql
Synonyms
Deprecated Radish 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?

The radioallergosorbent test, commonly called RAST, is a blood test that detects allergen-specific IgE antibodies. This form of the test is deprecated and is now used less often than other allergy-testing approaches.

Why might I need this test?

RAST may be used to investigate suspected allergies to foods, pollens, dust mites, animal dander, insect venoms, or other substances. Your clinician may use it when symptoms or other allergy tests need further evaluation.

How is the test performed?

A blood sample is tested against selected allergens, and the laboratory measures whether allergen-specific IgE is present. The original RAST method used a radioactive label, but testing methods and availability may vary.

How do I prepare for the test?

No special preparation is usually required for this blood test. Continue taking your medicines unless your clinician gives you different instructions, and tell the clinician about any recent allergy testing or treatments.

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

RAST allergy test

Frequently asked questions

Does a positive RAST result mean I am definitely allergic?
No. It shows an immune response to the tested allergen, but your clinician must consider whether that response matches your symptoms and other findings.
Is RAST still commonly used?
RAST is an older method and is considered deprecated in this form. Other blood or skin allergy tests may be preferred depending on the suspected allergy.
Do I need to stop taking allergy medicines before this test?
No special preparation is generally needed for RAST, and antihistamines usually do not affect this type of blood test. Follow any instructions provided by the ordering clinician.
  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