Influenza Ag

Keywords: Influenza antigen, Influenza virus antigen

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.