Skip to content

Allergen-Specific IgE, Serum — Radioallergosorbent Test (RAST)

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

This blood test measures allergen-specific IgE antibodies to help identify possible triggers of allergy symptoms.

Quick summary

["A positive result suggests an immune sensitization to the tested allergen but does not by itself confirm a clinical allergy."]

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

Key facts at a glance

LOINC
102975-0
Short code
Rat Epith+Ser+Ur IgE RAST
Synonyms
Rat Epith+Ser+Ur IgE RAST
Category
urine
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
Method
rast
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, also called a radioallergosorbent test or RAST, measures IgE antibodies directed against particular allergens. It is usually performed on serum obtained from a blood sample.

Why might I need this test?

A clinician may order this test to help evaluate sneezing, wheezing, hives, or other symptoms that may be related to an environmental or food allergen. The results can guide allergy testing, avoidance planning, or treatment decisions.

How is the test performed?

Your blood is drawn, and the serum is exposed to selected allergens. If IgE antibodies against an allergen are present, the laboratory can measure or classify that response.

How do I prepare for the test?

No special preparation is usually required for a routine blood draw. Some antihistamines can affect results, so tell the clinician and laboratory about any medicines or supplements you are taking and follow their instructions about pausing them.

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

Allergen-specific IgE (RAST)

Frequently asked questions

Does a positive RAST result mean I am allergic?
Not necessarily. It shows that IgE directed against the tested allergen was detected, so the finding should be interpreted with your symptoms, medical history, and other allergy tests.
Can this test identify the cause of my symptoms?
It can identify possible allergen sensitization, but the results may need to be confirmed or narrowed down through clinical evaluation.
Is serum the only specimen used for RAST?
RAST is conventionally performed on serum from a blood sample. If your order specifies a different specimen, confirm the collection instructions with the laboratory.
  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