Infectious Disease
Influenza A and B
Influenza A and B point-of-care testing detects influenza viral antigen or viral RNA in a respiratory swab to support rapid diagnosis of seasonal flu near the patient. Results are qualitative, reporting whether influenza A and influenza B are detected rather than a numeric concentration.
Why it is measured
Fast flu results help clinicians decide on antiviral treatment, infection-control measures and patient cohorting during the respiratory season. Timely detection can also reduce unnecessary antibiotic use and onward transmission.
| Typical range | Qualitative result, not a numeric value: in an adult without infection the expected report is Influenza A not detected (negative) and Influenza B not detected (negative). A positive result names the virus type detected. No measurement units apply, and analytical sensitivity varies by method, with molecular (nucleic acid amplification) assays generally more sensitive than antigen assays. |
|---|---|
| Sample | Nasal or nasopharyngeal swab. Some molecular point-of-care assays also accept swabs eluted in viral transport medium. |
| Turnaround | Antigen analysers: approximately 10 to 15 minutes. Molecular point-of-care assays: approximately 13 to 30 minutes depending on the platform, with some systems flagging an early positive sooner. |
Point of care devices that report it
- Abbott ID NOW Influenza A & B 2 (isothermal nucleic acid amplification)
- Roche cobas Liat Influenza A/B (RT-PCR)
- Cepheid Xpert Xpress Flu (GeneXpert, RT-PCR)
- BD Veritor System Flu A+B (digital immunoassay analyser)
- Quidel Sofia 2 Influenza A+B FIA (fluorescent immunoassay analyser)
- Abbott BinaxNOW Influenza A&B (rapid antigen card)
Questions, answered
Does a negative rapid flu test rule out influenza?
Not completely. A negative result, particularly from an antigen test, does not fully exclude influenza, especially when flu is circulating widely or the sample is taken late in the illness or from a poorly collected swab. Molecular point-of-care assays are more sensitive, and clinicians may repeat testing or act on clinical and epidemiological grounds where suspicion is high. This is general educational information and not advice for any individual.
What is the difference between antigen and molecular point-of-care flu tests?
Antigen tests detect viral proteins and are quick and lower cost but less sensitive. Molecular tests use nucleic acid amplification to detect viral RNA and are generally more sensitive and specific. Both report a qualitative positive or negative result for influenza A and B rather than a number.
Can these tests tell influenza A apart from influenza B?
Yes. These platforms report influenza A and influenza B separately, so the result shows which type, if any, is detected. They do not subtype influenza A (for example H1 versus H3); subtyping is performed by a reference laboratory.