Understanding your influenza test results is an important step in managing your health and preventing further spread of the virus. Influenza, commonly known as the flu, is a respiratory infection caused by viruses that can lead to symptoms like fever, body aches, and cough. Testing helps determine if influenza is the cause of your illness, guiding appropriate actions for your well-being and the health of those around you. Knowing what your test results signify empowers you to make informed decisions about care and isolation.
Common Influenza Test Types
Several methods detect the influenza virus, varying in speed and accuracy. Two primary categories of influenza tests are Rapid Influenza Diagnostic Tests (RIDTs) and molecular tests.
RIDTs, including rapid antigen tests, identify specific viral proteins, or antigens, in a respiratory sample. These tests provide quick results, often within 15 to 30 minutes, making them common for at-home use and in clinical settings where rapid decisions are needed.
Molecular tests, such as Reverse Transcription-Polymerase Chain Reaction (RT-PCR) assays, detect the genetic material of the influenza virus. These tests are more sensitive and specific than RIDTs, accurately identifying the presence or absence of the virus. While some molecular tests offer rapid results, others require samples to be sent to a laboratory, taking several hours to days. The choice of test depends on the clinical situation and the need for quick results versus higher accuracy.
Interpreting Your Test Results
Interpreting your test results is straightforward. Most rapid influenza tests display results using lines or symbols. On these tests, a control line (often marked “C”) must appear to confirm the test functioned correctly. The presence of this control line is a prerequisite for interpreting any other lines that may appear.
A positive result means influenza viral antigen or RNA was detected in your sample. On a rapid test, this is indicated by the appearance of a test line (often marked “T” or specific lines for Flu A and Flu B) in addition to the control line. A positive result suggests you likely have an influenza infection. A positive result, especially from a rapid test, indicates the detection of viral components but does not always mean a viable, infectious virus is present.
A negative result means the test did not detect influenza viral antigen or RNA. On a rapid test, this is shown by only the control line appearing, with no test line visible. While a negative result suggests you may not have the flu, it does not entirely rule out an infection. Other viruses or bacteria could be causing your symptoms, or the test might have missed a low viral load.
An invalid result means the test did not work properly and the result cannot be verified. This occurs when the control line does not appear. Reasons for an invalid result include improper sample collection, inadequate sample volume, or issues with the test kit itself. If you receive an invalid result, discard the test and retest with a new kit and a fresh sample.
Factors Affecting Test Reliability
No influenza test is completely accurate; several factors influence the reliability of your results. The timing of the test relative to when symptoms began plays a significant role. Tests are most accurate when the sample is collected within the first three to four days of symptom onset, as this is when the viral load is highest. Testing too early or too late in the illness can lead to a false negative result, where the test indicates no infection, but the virus is actually present.
The type of test used also affects reliability. Molecular tests, like RT-PCR, have higher sensitivity and specificity compared to rapid antigen tests. Rapid antigen tests, while convenient, have a greater chance of producing false negative results, especially when influenza activity is high. False positive results, where the test indicates flu but there is no infection, are more likely with rapid antigen tests when influenza activity is low.
Proper specimen collection impacts accuracy. An incorrectly collected sample, such as not swabbing deep enough or not rotating the swab adequately, can lead to inaccurate results, including invalid tests. Excessive mucus or the use of nasal sprays before testing can also interfere with the test’s performance. Following the manufacturer’s instructions for sample collection precisely is important for obtaining the most reliable outcome.
Next Steps After Receiving Results
After receiving your influenza test results, the next steps depend on the outcome. If you have a positive result, isolate yourself to prevent spreading the virus to others. This involves staying home until your fever has resolved for at least 24 hours without fever-reducing medication and your symptoms are improving. Managing symptoms with rest, hydration, and over-the-counter remedies can help with recovery. Individuals at high risk for severe illness or those experiencing worsening symptoms should contact a healthcare provider, as antiviral medications may be an option if started early in the illness.
If your test result is negative but you continue to experience flu-like symptoms, monitoring your symptoms is important. A negative result does not completely rule out influenza, especially if it was a rapid antigen test. Continue practicing good hygiene, such as frequent hand washing and covering coughs and sneezes, to prevent the spread of any respiratory illness. If symptoms persist or worsen, or if you are concerned, consulting a healthcare provider is recommended, as further testing, such as a molecular test, might be appropriate.
For an invalid test result, retest with a new kit. An invalid result means the test did not process correctly, and no reliable conclusion can be drawn from it. If repeated invalid results occur, or if you have any questions about your results or symptoms, seek guidance from a healthcare professional. They can provide personalized medical advice, diagnosis, and discuss treatment options.