What does a faint line on lateral flow test mean? Covid test results explained - and rules if it’s positive

The highly transmissible BA.2 sub-variant of Omicron is fuelling Covid infections across the UK

Covid cases are rising once again across the UK, with the current high rates being fuelled by the BA.2 sub-variant of Omicron.

The strain, which has been dubbed ‘Stealth Omicron’, has a faster rate of transmission than the original Omicron variant and is around 1.4 times more infectious.

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Stealth Omicron now accounts for the majority of infections across the country, according to the Office for National Statistics (ONS), but it is not thought to cause more severe illness.

The increased social mixing since following the easing of Covid restrictions is also thought to have contributed to the increase in infections, along with the waning effectiveness of the vaccine booster, particularly as older people received their top-up dose six months ago.

Despite the rising case numbers, Health Secretary Sajid Javid has insisted that the recent sharp rise in cases has not changed the government’s “level of concern” over the virus, but said that the data will be kept “under review”.

Symptoms of the BA.2 sub-variant are thought to manifest more quickly than previous strains, usually appearing within two days of being infected, with common signs including a runny nose, fatigue, headache, dizziness, fever and chills.

If you suspect you might have Covid, here’s how to interpret lateral flow test results and what to do if it comes back positive.

What does the ‘C’ and ‘T’ mean on a lateral flow test?

A lateral flow test result is interpreted by the two letters on the device where the swap sample is dripped on to.

Above the ‘S’ where the sample goes, there is a section above with the letters ‘C’ and ‘T’ to the right.

If a red line appears next to the C, this means the test is negative.

A test which returns no red lines at all, or just one line next to the T, means it is void and a new one will need to be taken on a fresh kit.

If your test returns two red lines - one next to the C and one next to the T - this means that it is a positive result and you had Covid-19 when it was taken.

What does it mean if the red line is faint?

If your lateral flow test returns a red line next to the C and a faint line next to the T, it is likely that this is a positive result - even if the T line is barely visible.

London-based A&E doctor Nathan Hudson-Peacock warned that any line which appears within the interpretation window - which is usually 30 minutes, but the leaflet inside the test box should confirm how long - is classed as a positive test.

A faint line next to the T is likely that this is a positive result

The doctor shared a picture of a test with a very faint positive line on his Instagram page earlier this month and explained in a post: “Essentially, if *any* line appears before the end of the interpretation window 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."

"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.

"Therefore, the most sensible next step, in my opinion, is not to isolate unnecessarily and not to book a PCR (makes it harder for people who genuinely need them to get one), but to be extra careful with precautions (social distancing, hand washing and mask wearing), and to continue testing with [lateral flow tests] as per NHS guidance."

When should I self-isolate?

If you feel unwell or have any coronavirus symptoms, you should take a lateral flow test to check if you have the virus.

If you do test positive, the self-isolation period differs depending on where you live in the UK.

Those who live in England and Northern Ireland are not legally required to self-isolate after testing positive, but government guidance strongly recommends staying at home for at least five days and avoiding going into work. However, this is no longer enforced by law.

In both Scotland and Wales, it is currently still a legal requirement to self-isolate after testing positive for Covid.

Those who test positive for coronavirus in Scotland should self-isolate for 10 days, although they can stop on the seventh day if they record two negative lateral flow tests on consecutive days.

People without symptoms continue to be advised to test twice weekly, close contacts of a positive case should test daily for seven days, and those with symptoms should get a PCR test.

In Wales, the isolation period is five full days, providing two consecutive lateral flow test results are produced 24 hours apart.

If you get a positive result on day five, you must then get a negative test on day six and day seven before leaving isolation. This process must continue until you get two negative results in a row up to the end of day 10.

You cannot leave quarantine earlier than the full 10 day period if you do not get two consecutive negative tests, regardless of your vaccination status.

Self-isolation rules in Wales will cease being law on 28 March.

From that date, the availability of free PCR tests for the public will end and be replaced with lateral flow tests for people with symptoms, which will be available until June.

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