Lateral flow tests are more accurate than first thought, according to research from University College London (UCL).
The government says regular testing is essential to stop the spread of Covid now that restrictions have eased across most of the UK.
How reliable are lateral flow tests?
When lateral flow tests (LFTs) were first trialled in Liverpool last year, they were criticised for being less reliable than polymerase chain reaction (PCR) tests, which are analysed in a lab.
But when UCL researchers used a new formula to calculate the rapid tests’ accuracy, they found LFTs were:
- More than 80% effective at detecting any level of Covid-19 infection
- Likely to be more than 90% effective at detecting who is most infectious
This is much higher than previously thought.
Current government guidance across the UK says people must get a follow-up PCR test after a positive LFT to confirm they have Covid – and can end their self-isolation if they get a negative PCR result.
But lead study author Prof Irene Petersen says people who get positive LFT results “should trust them and stay at home”.
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How do the tests work?
Lateral flow tests and PCRs do different things:
- LFTs pick up the most infectious people by detecting material from the surface proteins of the virus
- PCRs detect genetic material of the virus which can be present in the body for several weeks after somebody is actually capable of passing it on
Both tests involve swabbing your nose and/or throat.
But LFTs – also known as rapid tests – can be done at home, and show results in 20-30 minutes. PCR test swabs must be sent to a lab for analysis, with results provided in 24-48 hours.
What if I test positive?
Under the current system, if you get a positive LFT result, you have a legal obligation to self-isolate immediately, as does any adult in your household who is not fully vaccinated.
You must get a PCR test as soon as possible to confirm the result.
This can be booked online, or by calling 119 in England, Wales or Northern Ireland, or 0300 303 2713 in Scotland.
If you receive a negative follow-up PCR test result (if taken within two days of the positive LFT), you can stop self-isolating.
However, you must continue to self-isolate if the PCR result is positive, you choose not to take a follow-up PCR or the test was taken more than two days after the positive LFT.
How do I get a lateral flow test?
Regular lateral flow testing is widely used across the UK for frontline NHS and care home workers, school staff and secondary school pupils and in many other workplaces.
If you test at home, you are asked to report your results online or by calling 119.
Patients in England can see all registered test results in the NHS Covid app as well as details of their vaccination status.
Anyone in Scotland can order LFTs online or collect them from local testing centres.
Any businesses with 10 or more employees can also get LFTs for their staff.
People without symptoms in Wales can order tests online or collect them from most pharmacies.
All businesses in Northern Ireland can get LFTs for their staff.
What if I have Covid symptoms?
Anyone across the UK who has Covid symptoms – a new continuous cough, high temperature, or change in sense of taste or smell – also has a legal obligation to self-isolate immediately.
You must do a PCR test as soon as possible. You can order a test kit to be sent to your home or book an appointment at a walk-in or drive-through test site.
You must not leave home until you get your test results, except to post a test kit or for a PCR test appointment.
What about tests for travelling?
You may need to take a Covid test before travelling to your destination, or on your return.
You cannot use NHS-provided LFTs or PCRs for this purpose, and must buy tests from private providers.
Passengers who are under-18, or who have been fully vaccinated in the UK, the EU, the US, and many other recognised countries no longer have to take a Covid test before travelling to Britain, unless they have been in a red-list country.
All travellers, with the exception of children under the age of five, must still undergo a PCR test two days after arrival, which must be scheduled ahead of time.
The government has announced that fully vaccinated visitors to England will no longer be required to take the day two PCR test beginning at the end of October. Instead, they will be able to undergo a less expensive and simpler lateral flow test.