Reading results outside of the specified window
The majority of tests must be allowed to develop for 30 minutes, though some makes have a shorter window of around 15 minutes.
Reading results before the test has had enough time to develop could lead to a false negative.
Gov.uk states: “Wait 30 minutes before you read your result.
“Waiting the full 30-minute development time before you read your result is very important.
“A positive result can appear at any time after 20 minutes, however, you must wait for the full 30 minutes to record a negative result as the test line (T) may take this long to appear.”
Similarly, one doctor has warned people not to return to tests after the specified development window, as the test could become contaminated during this time.
London-based A&E doctor Nathan Hudson-Peacock shared a picture of a test with a barely noticeable positive line on Instagram.
He said: “If a faint line appears after the interpretation time window, then this does not count as a positive result and you do not need to book a PCR or self-isolate (unless, of course, you have symptoms in which case you must isolate and book a PCR regardless of what the LFT result is).”