What counts as a positive result on lateral flow test and what getting a faint line means

LATERAL flow tests have become an everyday staple for some people.

As you sit and wait for the result to be processed it's important to know what actually counts as a positive test.

Taking regular lateral flow tests is one of the best ways to protect yourself and others from Covid as it helps stop the spread of the virus.

Around 90 per cent of infections are Omicron cases – with many people experiencing cold-like symptoms.

A string of hugely positive studies show Omicron IS milder than other strains, with the first official UK report revealing the risk of hospitalisation is 50 to 70 per cent lower than with Delta.

Covid booster jabs protect against Omicron and offer the best chance to get through the pandemic, health officials have repeatedly said.

The Sun's Jabs Army campaign is helping get the vital extra vaccines in Brits' arms to ward off the need for any new restrictions.

Supplies of lateral flow tests have been running low this week as people scramble to get hold of them ahead of New Year.

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But what if you have taken a test and the line is faint, or if no line shows up at all? Here's all you need to know on what counts as a positive lateral flow test.


Posting a photo of a vaguely positive lateral flow to Instagram, London-based A&E doctor Nathan explained what it could mean.

He said: “Essentially, if *any* line appears before the end of the interpretation window (check leaflet, usually this is 30 minutes), then this is a *positive* test and you must isolate and book a PCR. 

“However, if a line appears *after* the interpretation window then this does NOT count as a positive test. You do not need to isolate and you do not need to book a PCR.”

But if you have symptoms, regardless of the lateral flow test result, you should isolate and book a PCR test, he said.


Even though most of us have now taken a lateral flow test at some point, it's important to always read the instructions.

This is because tests are made by different manufacturers and could have different requirements to make sure they are being done correctly.

For example, some tests require you to do both a mouth and nose swab – while some just require a nose swab.

But if you've accidentally gone over the 30 minutes, for example if you did a test before bed and forgot about it and there is a very faint bottom line, what should you do?

Nathan gave his views that: “If the faintly positive line appears after the time window, the most likely cause is either that there has been some contamination (e.g. food or drink, or some other very weak contaminant that is causing a false positive), or there are just incredibly low levels of the virus.

“If it is the latter, and obviously assuming you are asymptomatic at this point, then you are very unlikely to be a transmission risk anyway and so it is of little significance.”

Although NHS guidance says you do not need to self isolate if your lateral flow test is negative, if you have a faint positive line, Nathan advised to taken extra precuations.

He suggested to social distance, hand wash and wear your mask and continue testing with LFTs as per NHS guidance.

It is probably worth doing more lateral flow tests in the days following to see if the result becomes stronger.

A change from negative to positive can occur within hours, experts have shown.

You must report all lateral flow test results to the NHS.


You've done your swab and now it's time to put the droplets on the test.

But what if no lines at all show up on the test?

If nothing at all happens then the test is void and you should take another one.

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