Published Date: Dec 2023


Influenza or flu is a contagious respiratory illness caused by influenza viruses. The most common symptoms of flu include fever, cough, sore throat, runny or stuffy nose, body aches, headache, chills and fatigue. While most people get better within a week or two without requiring medical attention, influenza can cause severe illness or even death, especially in high-risk groups like children, elderly people and those with underlying medical conditions. Traditionally, diagnosis of influenza involves laboratory testing of nasal or throat swabs which takes at least a few days to process and get the results. However, rapid influenza diagnostic tests (RIDTs) provide a faster alternative to diagnose influenza with results available within 30 minutes.

What are Rapid Influenza Diagnostic Tests?

Rapid influenza diagnostic tests, also known as rapid flu tests, are medical device kits used to detect influenza A and B viruses directly from respiratory specimens like nasal or throat swabs. They are antigen-based diagnostic tests that provide qualitative results by detecting viral nucleoprotein antigens from patient samples. Unlike traditional virus culture or reverse transcription polymerase chain reaction (RT-PCR) methods, RIDTs do not require specialized laboratory equipment or techniques. The test is performed similar to a pregnancy test where the specimen is applied to the sample well of a test device which then indicates a positive or negative result within 10-30 minutes.

Types of Rapid Influenza Diagnostic Tests

There are different types of RIDTs available based on the detection method used:

- Immunofluorescence assays: Visualized using a fluorescent microscope to detect viral antigens.

- Immunochromatographic assays: Similar to pregnancy tests using labelled antibodies to produce a visible coloured line to indicate a positive result.

- Optical immunoassays: Use optical detection methods like colloidal gold labelling to generate a measurable signal proportional to the amount of antigen present.

- Nucleic acid amplification tests: Utilize RT-PCR, transcription-mediated amplification or other methods to exponentially amplify and detect viral RNA but provide results in 30 minutes to an hour.

The most commonly used RIDTs employ immunochromatographic technology due to its ease of use at the point-of-care without requiring specialized equipment or expertise to perform and interpret the test.

Advantages of Rapid Influenza Diagnostic Tests

- Convenience and speed: RIDTs can be used anywhere and provide influenza test results within 30 minutes compared to days required by laboratory tests.

- Timely treatment: Rapid diagnosis allows timely administration of antiviral medication within 48 hours of symptom onset for high-risk patients when treatment may be most effective.

- Infection control: Quick identification of positive patients helps implement appropriate infection control measures to limit the spread of influenza in healthcare settings.

- Cost-effectiveness: While the kits cost more than traditional tests, RIDTs can reduce unnecessary antibiotic use, hospitalizations and overall healthcare costs by facilitating early treatment decisions.

- Point-of-care testing: RIDTs enable diagnosis and management of influenza at the point-of-care in physician offices, urgent care centers, emergency rooms without waiting for laboratory results.

Performance of Rapid Influenza Diagnostic Tests

While RIDTs offer convenience of rapid results, their performance is not as high as laboratory-based molecular assays. Some key performance metrics of RIDTs include:

- Sensitivity: Ranges from 50-70% depending on the specimen type and viral load, which means around 30-50% of true influenza cases may be missed. Low viral shedding early in infection also affects detection.

- Specificity: Generally high at 90-95% so false positives are rare. Cross-reactivity with other respiratory viruses is low.

- Positive predictive value: Moderate to high when influenza is circulating widely in the community during peak seasons.

- Negative predictive value: Low to moderate. Negative results still require confirmation with other tests if clinical suspicion for influenza is high.

Proper clinical interpretation taking pre-test probability into account and use of more accurate follow-up tests helps maximize the diagnostic value of RIDTs.


In summary, while not as sensitive as molecular assays, rapid influenza diagnostic tests provide a simple and quick way to diagnose influenza at the point-of-care within 30 minutes. Their timely results help guide clinical management and infection control decisions. With good understanding of performance strengths and limitations, RIDTs remain an invaluable tool for influenza diagnosis, especially during peak seasons and outbreak investigation. Further improvements in test sensitivity without compromising speed would make RIDTs even more useful diagnostic aids for physicians worldwide.