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Allergen-Specific IgE Antibody (RAST), Qualitative

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

This legacy test checks a blood sample for IgE antibodies directed against specific allergens, helping assess possible allergic sensitization.

Quick summary

["A reactive result suggests the person has allergen-specific IgE antibodies, but clinical symptoms are needed to confirm allergy."]

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

Key facts at a glance

LOINC
21065-8
Short code
Deprecated A alternata IgG RAST Ql
Synonyms
Deprecated A alternata IgG RAST Ql
Category
liver
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
7
Ref high
56
Critical range
— – 500 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
84484
SNOMED
302773008
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, also known by the laboratory method RAST, looks for IgE antibodies directed against particular allergens. These antibodies are part of the immune response associated with immediate-type allergies. This is a deprecated or legacy form of allergen testing.

Why might I need this test?

A clinician may order this test when symptoms suggest an allergy but the suspected trigger is unclear. It may be considered when skin testing cannot be performed or when a blood test is more practical.

How is the test performed?

A blood sample is analyzed in the laboratory for antibodies against selected allergens. A qualitative report identifies the tested allergens as reactive or nonreactive rather than providing numerical measurements.

How do I prepare for the test?

Fasting is generally not required, but follow any instructions provided by the ordering clinician. Tell the clinician about major illnesses, recent allergic reactions, and all medicines or supplements you are taking.

Reference range

Adult males: 7-56 U/L; Adult females: 7-43 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

Allergen-Specific IgE (RAST)

Frequently asked questions

Does a reactive RAST result mean I am definitely allergic?
No. It shows that the blood contains IgE antibodies to the tested allergen, which can be associated with allergy but may also occur without symptoms.
What symptoms are commonly linked to immediate-type allergies?
Typical symptoms include sneezing, runny nose, wheezing, hives, swelling, or other reactions that develop soon after exposure. A clinician should interpret the result in context.
Can this test identify the cause of my symptoms?
It can identify sensitization to specific tested allergens, but it may not identify every possible trigger. Your clinician may recommend additional testing based on the results.
  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