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Trout-Specific IgG Radioallergosorbent (RAST) Test — Qualitative (Deprecated)

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

A deprecated qualitative test that detects IgG antibodies to trout. It indicates immune exposure but does not, by itself, diagnose trout allergy.

Quick summary

["A positive result shows trout-specific IgG antibodies but is not proof of a harmful allergy to trout."]

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

Key facts at a glance

LOINC
21581-4
Short code
Deprecated Trout IgG RAST Ql
Synonyms
Deprecated Trout 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?

This is a qualitative laboratory test designed to detect IgG antibodies directed against proteins from trout. RAST is an older testing method, and this version of the test is considered deprecated.

Why might I need this test?

It may have been used to evaluate whether a person had an immune response to trout after eating it or being exposed to it. Food-specific IgG testing is not considered a reliable stand-alone test for diagnosing food allergy.

How is the test performed?

The laboratory uses the RAST method to determine whether trout-specific IgG antibodies are present. The result is reported qualitatively as detectable or not detectable, depending on the laboratory's method.

How do I prepare for the test?

Follow the laboratory's instructions before testing. Because preparation requirements can vary, ask the laboratory whether fasting, medication changes, or avoidance of trout before the sample is collected is necessary.

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

Trout IgG RAST, Qualitative

Frequently asked questions

Does a positive trout IgG RAST result mean I am allergic to trout?
No. Trout-specific IgG can occur in people who tolerate trout and does not establish a harmful allergic reaction. Allergy evaluation should be based on symptoms and, when appropriate, skin-prick testing or other clinician-directed methods.
Why is this test described as deprecated?
This version of the test is no longer considered a preferred method for evaluating suspected food allergy. A clinician can recommend more appropriate testing based on the person's reaction history and examination.
What should I do if I have symptoms after eating trout?
Seek urgent medical care for trouble breathing, throat swelling, faintness, or other signs of a severe reaction. For less severe symptoms, discuss the episode with a clinician or allergist rather than relying on an IgG test result.
  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