From the Guidelines
Point-of-care (POC) influenza tests are most effective when performed within the first 3-4 days after symptom onset, with optimal results within 48-72 hours, as the sensitivity of these tests decreases significantly after this period 1. When considering the detection of influenza A or B using POC tests, it's crucial to understand that the timing of the test is critical for accurate results.
- The highest viral shedding occurs during the early period of symptom onset, making detection more reliable.
- After the initial 3-4 day window, the sensitivity of POC tests decreases significantly as viral load diminishes, even though the patient may still be symptomatic.
- The sensitivity of these rapid tests ranges from approximately 50-70% compared to more definitive methods like PCR, with this sensitivity dropping further as time from symptom onset increases 1. Key factors to consider when interpreting POC influenza test results include:
- The level of influenza activity in the community
- The positive and negative predictive values of the test
- The potential for false negatives, particularly beyond the 4-day mark If testing is performed later in the illness course and clinical suspicion remains high despite a negative result, more sensitive testing methods like PCR should be considered, or treatment decisions may need to be based on clinical judgment rather than test results 1.
From the Research
Detection of Influenza A or B using POC Influenza Test
- The detection of influenza A or B using a POC influenza test is highly specific but less sensitive, detecting 65-77% of specimens confirmed as positive on culture, direct immunofluorescence or PCR testing 2.
- A positive test is useful for directing initiation of therapy in the clinician's office and making a positive diagnosis of influenza in patients with influenza-like clinical syndromes 2.
- The test should be used within 48 hours of symptom onset for optimal results, as antiviral agents are most effective when started within this timeframe 3, 4, 5.
Timing of POC Influenza Test
- The POC influenza test can detect influenza A or B within 48 hours of symptom onset, but the exact timing may vary depending on the type of test used and the individual patient's symptoms 2, 6.
- Rapid point-of-care PCR influenza testing has been shown to have a high sensitivity and specificity, with >95% sensitivity and specificity compared to centralized PCR assays 6.
Clinical Impact of POC Influenza Test
- The use of a POC PCR test for influenza has been shown to improve antiviral prescribing practices compared to traditional RIDT, with antiviral prescribing being lower in patients with a negative POC PCR result 6.
- The POC PCR test can help reduce unnecessary antibiotic prescriptions and improve patient outcomes by providing rapid and accurate diagnosis of influenza 6.