Lateral Flow Tests

a faint line for lateral flow tests

June 14, 2022

lateral Flow Tests

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

Covid 19 appears to be on the up again in the UK.

Rising once again across parts of the UK.

With the newer BA.4 and BA.5 Omicron variants thought to be causing the increase..

Infections with Covid 19 compatible with the original Omicron BA.1 strain have also seen a jump, but the highly infectious BA.2 variant still remains the most prevalent strain in the UK.

797,500 people in households in England were estimated to have tested positive for Covid in the week to 2 June

  • the equivalent of around one in 70 of the UK population, the Office for National Statistics (ONS) said.

Up week on week from 784,100, which was also about one in 70.

London, north-west England and south-east England have all seen sharp rises. While eastern England has also shown early signs of an increase.

Wales has seen Covid cases increase very slightly to 40,500 people, up from 39,600. Both estimates are equivalent to around one in 75 people and the ONS describes the trend here as “uncertain”.

Meanwhile, separate figures show the recent fall in the number of people in hospital with the virus may have come to a halt.

A total of 4,602 patients in England had Covid on 13 June, up 12% on the previous week, while in Wales the figure appears to have levelled off at around 250 to 260. A steady downwards trend since early April of patients in hospitals, following the peak of the Omicron BA.2 wave. These patient numbers remain well below the levels reached in all previous outbreaks. Omicron variant symptons appear to occur quicker. They are thought to able to be expressed more quickly than previous strains. Appearing 2 days of being infected. With common signs including a runny nose, fatigue, headache, dizziness, fever and chills.

Here’s how to interpret lateral flow test results and what to do if it comes back positive.

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

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

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

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

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

If your lateral flow test returns two red lines - one next to the C and one next to the T - 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.

Any line which appears within the interpretation window - around 30 minutes, ( inside the test box should confirm how long) - is classed as a positive test.


a line appearing 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." Just be be extra careful with precautions and to continue testing with lateral flow tests as per NHS guidance. In this instances, do one again as soon as you can.