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What does a faint line on lateral flow test mean?


Lateral flow test

Lateral flow test

Advice: Queen’s University virologist Dr Connor Bamford

Advice: Queen’s University virologist Dr Connor Bamford


Lateral flow test

A positive lateral flow test — no matter how faint — must be treated as a definite Covid-19 case as the home testing kits are “very reliable”, a Queen’s University virologist has said.

Lateral flow tests (LFTs) are designed to detect the presence of antigens found in the virus.

One pinkish red line next to the control marker C indicates a negative result. A second line next to the marker T is a sign of a positive result.

However, many people have reported a faint second line on their test result, while others have seen a bold line after testing positive.

Coronavirus Data Graphs

As part of the Executive’s efforts to reduce the transmission of the Omicron variant, the public has been encouraged to take an LFT, otherwise known as a rapid antigen test, before leaving home.

New rules around those who test positive for the virus has seen the isolation period cut from 10 days to seven — but only if you test negative on day six and day seven using a LFT.

Fully vaccinated close contacts must also test themselves every day during that period.

As a result of the increase in demand for LFTs, there is a shortage of the home testing kits and a lack of available slots for PCR tests at Northern Ireland’s drive through sites.

Queen’s University virologist Dr Connor Bamford said that no matter how faint the T line may be, you are more than likely carrying the virus, and booking a PCR is vital as it is the “gold standard” when confirming the presence of Covid-19.

“The LFTs measure roughly the amount of virus in the sample,” he explained. “The amount of that colour is roughly proportionate to how much virus you've got in that sample.

“A bigger, bolder line means more virus and a fainter line might mean less virus.

“However, in both cases you're likely to be infected. If the LFTs pick up anything, you are very, very likely to be infected.

“In a couple of hours it can go from very faint to very, very bold and so in both those cases you probably have enough virus to spread that on so you should be isolating and booking a PCR to confirm that.

“If you're seeing a faint band you should be treating it as positive. You are positive, you are infected, so if you can see anything on that LFT you should treat it like it is Covid and you should isolate.”

Dr Bamford said LFTs tell who is most likely to be contagious and infectious and are a great tool in the fight against Covid as they are so easy to use.

“LFTs are very helpful and very reliable especially looking at asymptomatic people and looking at who is more likely to be contagious,” he added.

UK Government advice on LFTs states “even faint lines” shows a test is positive.

“Lateral flow tests used by the UK Government go through a rigorous evaluation by the country’s leading scientists,” the official guidance says. “This means they are accurate, reliable and successfully identify those with Covid-19 who don’t show symptoms and could spread the virus without realising.

"Lateral flow tests are not being offered in isolation, but alongside a range of other measures to drive down cases and break chains of transmission.”

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