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Trichophyton IgG Antibody, Radioallergosorbent (RAST) — Qualitative

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

A qualitative blood test for IgG antibodies to Trichophyton, a fungus that causes ringworm and other skin, hair, or nail infections.

Quick summary

["A positive result shows prior exposure to Trichophyton, but it does not by itself confirm an active infection."]

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

Key facts at a glance

LOINC
33324-5
Short code
Deprecated Trichophyton IgG RAST Ql
Synonyms
Deprecated Trichophyton 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 test looks for IgG antibodies directed against Trichophyton, a group of fungi commonly associated with ringworm and other dermatophyte infections. A qualitative result is reported as positive or negative.

Why might I need this test?

It may be used to help evaluate suspected fungal infection of the skin, scalp, or nails, particularly when the diagnosis is uncertain. It is a legacy test and may no longer be routinely offered; a fungal culture or other testing may be recommended instead.

How is the test performed?

The laboratory analyzes the submitted blood sample for antibodies that bind to Trichophyton antigen. Older versions of this test used a radioallergosorbent assay method, which is included in the test name.

How do I prepare for the test?

No special preparation is usually required for a routine antibody blood test. Follow any instructions from your healthcare professional, and tell the laboratory if you have recently started antifungal medication.

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

Trichophyton IgG antibody (RAST)

Frequently asked questions

Does a positive result mean I have ringworm now?
Not necessarily. It shows exposure to Trichophyton, but antibodies can persist after an infection has cleared, so your symptoms and other tests are also important.
What does a negative result mean?
A negative result means detectable antibodies were not found at the time of testing. It may occur early in an infection, after immune responses decline, or when the infection is caused by a different fungus.
Is this test still commonly used?
This is marked as a deprecated test and may not be available at many laboratories. Your clinician can determine whether skin, hair, or nail fungal testing is more appropriate.
  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