What is an RT-PCR (or simply PCR) and an Antigen Lateral Flow test?
PCR (Polymerase Chain Reaction) is the gold standard for COVID-19 testing. PCR offers the most reliable results as it can detect small quantities of COVID-19 genetic material (RNA) in a sample. The test requires a sample that is normally collected from the nose and/or throat. Once the sample reaches the lab, a series of chemicals are added to it. If the virus is present a reaction occurs whereby many copies of viral genetic material are created, allowing for detection and analysis by scientists. This allows for the confirmation of whether or not the virus is present, and if someone is currently infected.
Antigen Lateral Flow Test (or simply Lateral Flow)
A Lateral Flow test is a quick and simple method to test people who do not have symptoms of COVID-19 but may still be spreading the virus. A Lateral Flow test allows for the detection of 'antigens' produced by the COVID-19 virus. With a Lateral Flow test, samples are analysed on the spot with a small device (like a home pregnancy test kit) that gives a result in 40 minutes. Lateral Flow tests can be carried out at home, with no need for further processing by a lab. If the result from the Lateral Flow test is positive, then an NHS PCR test must be carried out if you wish to update your medical records. A negative result does not guarantee that you do not have coronavirus (due to the viral load being below the level of detection).
ExpressTest use the Roche Biosensor Nasal COVID-19 Antigen Lateral Flow Rapid Test. The sensitivity and specificity rates for this test are:
Diagnostic Sensitivity: 96.52 % (95% CI: 91.33 % -99.04 %)
Diagnostic Specificity: 99.68 % (95% CI: 98.22 % -99.99 %)
Positive predictive value (PPV): 97.5 %
Negative predictive value (NPV): 98.3 % (95% CI: 94.0 % -99.5 %)