Influenza virus antigen

Last updated: Wednesday, 17, March, 2004
Item Process
Specimen

Nasal swab, nasal wash or aspirate, throat swab for IF.

Dry swabs, that is not in transport medium, are required for rapid immunoassays and should be tested within 1 hour of collection.

Dry swabs should also be collected for PCR testing.

Method

Nucleic acid detection by immunoassay, IF, nucleic acid detection after amplification (PCR).

Application

Nucleic acid detection by immunoassay allows point of care testing for rapid diagnosis of acute influenza due to influenza virus types A and B, and thus can be used to guide the use of antiviral treatment.

IF and PCR testing are more sensitive.

Interpretation

A positive result confirms infection with influenza types A and B.

Rapid immunoassays generally do not distinguish between types A and B, whereas IF testing may. 

Rapid immunoassays have a sensitivity of ~80%, so a negative result does not rule out the diagnosis.

False positives are uncommon.

Reference

Cox NJ and Subbarao K. Lancet 1999; 354: 1277-1282.