What is Flu (Influenza) Test?
A Flu (Influenza) Test is used to detect the presence of influenza viruses, which cause a contagious respiratory illness affecting the nose, throat, and sometimes the lungs. The test can identify whether your symptoms are caused by Influenza A, Influenza B, or, depending on the testing method, rule out influenza altogether. Since flu symptoms often resemble those of the common cold, COVID-19, and other respiratory infections, laboratory testing helps determine the exact cause of illness.
A Flu (Influenza) Test helps diagnose influenza, especially in people at higher risk of complications, including young children, older adults, pregnant women, and individuals with weakened immune systems or chronic medical conditions. Early diagnosis can help guide treatment decisions, determine whether antiviral medication may be beneficial, and reduce the spread of infection to others. The test may also be used during influenza outbreaks or when hospitalised patients present with severe respiratory symptoms.
How is the Test Performed?
Preparation
- Drink plenty of water the night before.
- You may be asked to not eat anything one or two hours before the test or stop taking antibiotics.
- Don’t stop taking medicines unless healthcare providers ask.
- In case of BAL and/or bronchoscopy, you may be asked to fast for up to 12 hours and stop taking
- certain medications depending on what your healthcare provider advises.
Collection
- All flu tests require a respiratory sample mst often from the nasal cavity. The exact steps depends on how your healthcare provider collects the sample.
- A sterile swab is gently inserted into one nostril to collect a sample from the nasal cavity or the back of the nose (nasopharynx).
- Or your healthcare provider might put saline in your nose and collect a sample of nasal fluid by gentle suction.
- In at-home tests, you swab your nostril according to the instructions on the kit, which might take 30 minutes to get the results.
Lab Analysis
The respiratory specimen is analysed using one or more laboratory methods, depending on the type of test requested. Common techniques include rapid influenza diagnostic tests (RIDTs), rapid molecular assays, and more. Molecular tests, such as RT-PCR, are generally the most accurate and can identify both Influenza A and Influenza B viruses. Laboratory results are interpreted alongside your symptoms, medical history, and physical examination to confirm or rule out influenza infection.
What are the symptoms that prompt this test?
A Flu (Influenza) Test is recommended when you have symptoms of influenza, particularly during the flu season or after close contact with someone who has the flu. Because influenza shares many symptoms with the common cold, COVID-19, and other respiratory infections, testing helps healthcare providers identify the cause of illness and determine the most appropriate treatment.
Your healthcare provider may recommend a Flu (Influenza) Test if you experience:
- Sudden onset of fever or chills
- Cough
- Sore throat
- Runny or stuffy nose
- Muscle or body aches
- Headache
- Fatigue or extreme tiredness
Weakness - Loss of appetite
A Flu (Influenza) Test may also be recommended if you:
- Are at high risk of developing flu-related complications
- Are aged 65 years or older
- Have a weakened immune system
- Have chronic conditions such as asthma, diabetes, heart disease, or kidney disease
- Develop severe or worsening respiratory symptoms
- Are hospitalised with suspected influenza
- Have been in close contact with someone diagnosed with influenza during an outbreak
- Are younger than age 5
What are Normal Ranges for This Test?
There’s no flu (influenza) test normal range. The results are reported as either positive, negative, or occasionally inconclusive, depending on the testing method used.
Common interpretations include:
- Negative: No influenza virus was detected in the sample.
- Positive: Influenza virus was detected in the sample.
Inconclusive or Invalid: The test could not provide a reliable result, and repeat testing may be required.
It is important to note that a negative result does not always rule out influenza, particularly if the sample was collected too early or too late in the illness, or if there was insufficient virus in the specimen.
“The reference ranges vary depending on the laboratory and the methodology used. Individuals must consult their healthcare provider for correct interpretation of the results.”
What Happens if Test Results Show Abnormal Levels?
Since a Flu (Influenza) Test detects the presence of influenza viruses rather than measuring a substance in the blood, the results are interpreted as positive or negative.
Positive Flu Test
A positive result indicates that the influenza virus was detected in your respiratory sample. Depending on the test, the result may identify Influenza A, Influenza B, or both.
If you test positive, your healthcare provider may recommend:
- Antiviral medication, particularly if treatment begins within 48 hours of symptom onset
- Rest and adequate fluid intake
- Fever-reducing or pain-relieving medications, if appropriate
- Staying home to help prevent spreading the virus to others
- Close monitoring if you are at high risk of complications
Negative Flu Test
A negative result means that influenza virus was not detected in the sample. However, it does not always mean you do not have the flu. False-negative results can occur if:
- The sample was collected too early or too late after symptoms began
- The specimen did not contain enough virus
- A less sensitive testing method was used
If influenza is still strongly suspected despite a negative result, your healthcare provider may recommend repeat testing, a more sensitive molecular test such as RT-PCR, or evaluate you for other respiratory infections, including COVID-19 or respiratory syncytial virus (RSV). Treatment decisions will depend on your symptoms, medical history, risk factors, and overall clinical assessment.
Need a Flu (Influenza) Test? Book your appointment today for fast and accurate influenza testing by our experienced laboratory professionals.
