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Influenza Virus Antigen Test

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

Detects influenza viral antigens to help identify an active influenza infection. The test is generally performed on a respiratory specimen, although the abbreviated code does not clearly specify the exact specimen or method.

Quick summary

["A positive result generally supports a current influenza infection, while a negative result does not completely rule it out."]

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

Key facts at a glance

LOINC
99356-8
Short code
Flu vacc last 12Mo
Synonyms
Flu vacc last 12Mo
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?

An influenza virus antigen test looks for proteins from influenza virus in a patient sample, usually a respiratory specimen. It can help clinicians determine whether influenza is the likely cause of fever, cough, body aches, or other flu-like symptoms.

Why might I need this test?

Your clinician may order this test during flu season if you have symptoms consistent with influenza, especially if you are at higher risk of complications, are elderly, are pregnant, or have a weakened immune system. Early results can guide treatment and infection-control decisions.

How is the test performed?

A respiratory sample is collected and examined for influenza viral antigens using a laboratory method. The exact specimen and testing method are not fully identifiable from the abbreviated code.

How do I prepare for the test?

Ask your healthcare provider for collection-specific instructions. Depending on the specimen, you may be asked to avoid eating, drinking, or using nasal products for a short period before the sample is collected.

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

Influenza antigen test

Frequently asked questions

Does a positive influenza antigen test mean I have the flu?
A positive result generally supports an active influenza infection, but your clinician will interpret it with your symptoms and examination findings.
Can I have the flu if the test is negative?
Yes. A false-negative result can occur, particularly later in the illness when the amount of detectable virus has decreased, so another type of influenza testing may be considered.
Is this the same as a flu vaccine test?
No. An antigen test detects influenza virus in a patient sample; a flu vaccine is used to help prevent influenza infection.
  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