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Alpha-Lactalbumin-Specific IgE (RAST)

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

A blood test that measures IgE antibodies to alpha-lactalbumin, a cow’s-milk protein, to help evaluate possible milk allergy.

Quick summary

["A positive result suggests an immune response to alpha-lactalbumin but does not by itself confirm a milk allergy."]

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

Key facts at a glance

LOINC
102758-0
Short code
A-Lactalb IgG RAST
Synonyms
A-Lactalb IgG RAST
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
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, often called a RAST test, measures allergen-specific IgE antibodies directed against alpha-lactalbumin. Alpha-lactalbumin is a protein found in cow’s milk.

Why might I need this test?

It may be ordered when a person has symptoms suggestive of cow’s-milk protein allergy, such as hives, swelling, vomiting, abdominal pain, wheezing, or other allergic reactions. Results are interpreted along with symptoms, exposure history, and other allergy testing.

How is the test performed?

A blood sample is collected and tested in the laboratory for IgE antibodies to alpha-lactalbumin. RAST is a laboratory method that can be used to detect allergen-specific antibodies.

How do I prepare for the test?

No special preparation or fasting is usually required. Tell your clinician about any known milk allergy, recent reactions, medicines, and other tests that may affect interpretation.

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

Alpha-lactalbumin IgE

Frequently asked questions

What does a positive alpha-lactalbumin IgE result mean?
It means alpha-lactalbumin-specific IgE antibodies were detected, suggesting sensitization to this milk protein. It does not by itself prove a symptomatic milk allergy.
Does this test diagnose cow’s-milk protein allergy?
No. It can support allergy evaluation, but a diagnosis usually depends on symptoms, exposure history, and sometimes skin-prick testing or supervised food challenges.
Can I stop avoiding milk based only on this result?
Do not change a prescribed diet without medical guidance. Discuss the result with your clinician, particularly if you have severe prior allergic reactions or a history of anaphylaxis.
  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