Using Lateral Flow Tests

Using Lateral Flow (LF) tests to manage covid risks at your event

Along with vaccination, Lateral Flow tests are now a major, Government-recommended, way of reducing coronavirus risk in what might otherwise be higher-risk situations.  Using them can mean a safe return to, for example, singing and more normal-feeling lives.  To make good use of them, we need to understand what LF tests are good at (and not so good at).

Some of us have got used to thinking of PCR tests as the “proper” test and LF tests as second best and perhaps not worth doing.   But this is not true.   One test is not better than the other; they are useful for different purposes.

How to use Lateral Flow tests to keep your event safe from covid

  1.  Ask participants to take a test immediately they develop any possible respiratory symptom – for example, a runny nose, cough, sneezing or sore throat. LF tests are highly accurate during an individual’s most infectious state, which with the delta variant is typically when their body starts showing symptoms.   Omicron update: Because of how the omicron variant behaves in the first couple of days after exposure or first appearance of symptoms, it is recommended that Lateral Flow Tests be taken twice, once on the appearance of the symptoms and the second time 24-48 hours later.   This is to reduce the chances of a false negative.  Two negative tests mean that the cold symptoms are very unlikely to be caused by covid.


2.   Ask participants to test immediately or very soon before coming to an event, meeting or visit at which they are going to be mixing with people who are particularly vulnerable to covid, or unvaccinated people (all of whom are vulnerable) or at which they are going to be engaging in activities, such as singing or intensive exercise, that involve heavy breathing and make it hard or impossible to wear a mask.   LF tests are very good at identifying contagious individuals.    “Immediately or very soon” means as short an interval between test and event as possible, ideally within a few hours and certainly within 24 hours.   This is because the omicron variant builds up within the body of an infected person much more quickly than previous variants.  If an event organiser required all participants to test before coming, they’d pull out the great majority of contagious people.   If the participants are also all vaccinated (and, to protect against omicron, also boosted), the risk drops to a very low level.


  1. Encourage participants to test after possible exposure. Situations that involve getting together with a lot of people you do not normally see, such as a work conference, extended family party, funeral, make exposure to covid more likely.   Testing after you’ve participated and before you spend time with unvaccinated children or more vulnerable older adults adds an additional layer of protection.

About Lateral Flow (LF) tests

Lateral Flows work by looking for the virus proteins, that is by looking for evidence of active virus.   These tests are very accurate (around 95%) during the highly infectious period, whether a person is symptomatic or not; with Delta, that’s two to five days after exposure.   LFs can be run at home, produce results in about 15 minutes, are easy to do (once you get used to them) and are widely available at no cost.

On the other hand, they are not sensitive to very low viral loads – that is, at the very beginning of an infection, at a point when the individual is unlikely to be contagious, the test will return a “false negative”.  That is why people sometimes call LF tests “contagiousness tests”.

About PCR tests

PCR tests are more sensitive than LF tests.   They look for evidence of the RNA of the virus in your system and can detect even very small amounts of it.  They are therefore the go-to test for identifying someone who has been infected with covid, even if they are at a very early stage of the infection, with very little virus present as yet and no symptoms.

On the other hand, because they are so sensitive to very low viral loads, they’ll often return a positive result even after recovery, for weeks or, in rare cases, months after the person ceased to be contagious, because some residual (non-infectious) viral fragments remain.  In addition, they are expensive, require a lab, take one or more days to produce a result and are only available to people who meet quite narrow criteria (usually having one of the 3 “classic” symptoms of covid).