Lateral flow tests are more accurate in tracing Covid than first thought according to a new study.
The rapid tests, which provide users with a result in 30 minutes, have been previously criticised for being ‘inaccurate’.
Comparisons are often made with PCR tests, which takes a much longer time for a result as they are sent off to a lab for a closer investigation.
Lateral flow tests have become a key component in the fight against Covid – with Scots urged to test at home on two occasions every week.
Anyone who tests positive on a LFT must then book a PCR test, in accordance with current Scottish Government coronavirus rules.
This increases to 90% when detecting those who are most infectious, the study adds.
A person may test negative for Covid through a LFT but then go on to test positive on a PCR test if they are not at “peak transmissible stage”, the scientists said.
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They noted that the two testing methods should not be compared, as they work in different ways – with LFTs likely to give a positive result when someone is infectious.
PCR tests instead detect genetic material which can be present in the body weeks after the person is infectious.
Professor Michael Mina, from the Harvard School of Public Health, said LFTs could catch “nearly everyone” with Covid when they are at their most infectious.
He said: “There is a spectrum of infectious amounts of the COVID-19 virus and we show that LFTs are likely to detect cases 90-95% of the time when people are at their most infectious.
“The tests could achieve even 100% sensitivity when viral loads are at their peak and therefore catch nearly everyone who is currently a serious risk to public health.
“It is most likely that if someone’s LFT is negative but their PCR is positive then this is because they are not at peak transmissible stage.”
The study concluded that LFTs are a reliable tool in preventing the spread of Covid.
Everyone currently has free access to LFTs, with the tests being used widely to allow entry into schools, offices and work places.
Prof Irene Petersen, the lead study author, urged people to “trust them and stay at home” if they get a positive result.
She said: “Previous studies comparing the reliability of lateral flow tests and PCR tests could be potentially misleading because a PCR test is a marker of having been infected at some point within a certain window of time and does not necessarily mean someone is infectious when testing positive.”