Medical professionals can usually collect samples very quickly. However, people may have to wait for the results. While rapid tests take only around 15 minutes, slower tests may require an 8-hour wait.

Influenza, or flu, can be dangerous for older people, young children, and individuals with compromised immune systems.

Flu tests are important as they speed up the treatment process and help stop the flu from spreading.

This article examines how long flu tests take, test types, accuracy, and more.

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All flu tests involve taking a sample of bodily fluids to test in a lab. The sample collection should take less than a minute, but some procedures, such as those requiring a bronchoscope, can take up to several minutes.

Different flu tests use different sample collection methods, including:

  • Nasopharyngeal (NP) swab: This technique uses a swab that goes through the nose and into the nasopharynx to collect mucus. The nasopharynx is the uppermost part of the throat, which makes contact with the nasal cavity.
  • Nasal or throat swab: This collects mucus from the nasal cavity or throat.
  • Bronchial wash: This technique uses a bronchoscope, a thin tube that can enter the respiratory system. Doctors will place a saline solution into the bronchoscope before washing the airways. They will then use the bronchoscope to collect the washed mucus.
  • Nasopharyngeal (NP) wash: This is similar to a bronchial wash, but it does not use a bronchoscope and washes mucus from the nasopharynx.
  • Sputum: This technique involves collecting a sample of spit.
  • Nasal aspirate: This involves using a thin tube and suction device to suck mucus from the nasal cavity.
  • Endotracheal aspirate: Like a nasal aspirate, except that the mucus is from the windpipe, or trachea.

The table below summarizes the test types, collection methods, and general waiting times for results.

TestSample collection methodsTime to results
Rapid influenza diagnostic testsNP swab, nasal swab, and throat swabUp to 15 minutes
Rapid molecular assayNP swab and nasal swabBetween 15 and 30 minutes
ImmunofluorescenceNP swab or wash, bronchial wash, and nasal or endotracheal aspirateBetween 1 and 4 hours
Reverse transcription polymerase chain reaction (RT-PCR) and other molecular assaysNP swab, throat swab, NP or bronchial wash, and nasal or endotracheal aspirate, sputumBetween 1 and 8 hours
Rapid cell cultureNP swab, throat swab, NP or bronchial wash, nasal or endotracheal aspirate, and sputumBetween 1 and 3 days
Viral tissue cell cultureNP swab, throat swab, NP or bronchial wash, nasal or endotracheal aspirate, and sputumBetween 3 and 10 days

The Centers for Disease Control and Prevention (CDC) also explain how different types of tests work:

  • Molecular assays: These include rapid molecular assays, RT-PCRs, and other nucleic acid amplification tests. They detect RNA from the flu virus, a substance that only exists when the virus is replicating.
  • Antigen detection tests: These include rapid influenza diagnostic tests and immunofluorescence assays. The tests look for flu antigens — proteins on the surface of flu viruses that the immune system “recognizes” as a threat.
  • Viral cultures: These include rapid and viral tissue cell cultures. They involve providing the flu virus with an ideal environment to replicate. This allows public health officials to test them more thoroughly. However, viral cultures are not useful from a diagnostic perspective, as they take too long.

Research has shown that different flu tests vary in accuracy. The following table summarizes what scientists know about this, according to the CDC:

rapid influenza diagnostic testscan detect between 50% and 70% of flu infections
rapid molecular assaycan detect between 90% and 95% of flu infections
immunofluorescencecan detect between 37.5% and 41.5% of flu infections
RT-PCR and other molecular assayscan detect up to 98% of flu infections

A variety of locations can provide flu tests. These include doctor’s offices, hospitals, and some pharmacies.

An individual who thinks they may have the flu can discuss this with a doctor, who can recommend the best place for testing.

This section answers some frequently asked questions about flu tests.

How long does flu show up on PCR?

There is some variation in how long PCR tests take to detect flu. It all depends on the specifics of the sample and the test.

Generally speaking, such tests can take between 1 and 8 hours before showing a result.

How accurate is the rapid flu test?

There are two main types of rapid flu tests: rapid influenza diagnostic tests and rapid molecular assays.

Rapid influenza diagnostic tests can detect between 50% and 70% of flu infections. For rapid molecular assays, this figure is between 90% and 95%.

To perform flu tests, doctors must collect a sample. The sample collection process should only take a few moments.

Rapid influenza diagnostic tests and rapid molecular assays only take between 15 and 30 minutes to provide results.

Immunofluorescence, RT-PCR, and other molecular assays take between 1 and 8 hours. Viral cultures, which are not useful for diagnostic purposes, can take several days.