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Grapefruit-Specific IgG Antibody Test (RAST), Qualitative — Deprecated

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

A deprecated qualitative test for antibodies associated with grapefruit exposure or sensitivity; it should not be used by itself to diagnose food allergy.

Quick summary

["A positive result does not necessarily mean you have a grapefruit allergy."]

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

Key facts at a glance

LOINC
21315-7
Short code
Deprecated Grapefruit IgG RAST Ql
Synonyms
Deprecated Grapefruit 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 an older qualitative blood test intended to detect antibodies associated with grapefruit exposure or sensitivity. The compressed name includes IgG and RAST terminology, but the exact specimen and laboratory method cannot be confirmed from the test name alone.

Why might I need this test?

This test may appear in older medical records or allergy workups. It has been deprecated because antibody findings alone do not reliably show that grapefruit causes symptoms or that avoidance is necessary.

How is the test performed?

The archived test was qualitative, meaning it reported antibodies as detected or not detected rather than providing a reliable concentration. Because it is deprecated, it is generally not offered as a current stand-alone test.

How do I prepare for the test?

If you are discussing an old result with a clinician, bring the laboratory report and a list of symptoms that occur after eating grapefruit. Avoid stopping prescribed medicines unless your clinician advises you to do so.

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

Grapefruit IgG/RAST Test

Frequently asked questions

Does a positive result mean I am allergic to grapefruit?
No. A positive antibody result indicates that the test detected an antibody, but it does not prove that grapefruit causes your symptoms or that you have a true food allergy.
Why is this test marked deprecated?
The test is no longer recommended for routine allergy diagnosis because antibody results can be misleading and do not reliably predict symptoms. Clinicians generally rely on the medical history, food-allergy testing when appropriate, and sometimes supervised food challenges.
What should I do if my record shows a positive result?
Discuss the result and any symptoms with your clinician or allergist. Do not start avoiding grapefruit or other foods solely because of this result unless a qualified clinician recommends it.
  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