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Lateral flow test

Dr Karen Martin
Reviewed by Dr Karen MartinReviewed on 19.10.2023 | 3 minutes read

A lateral flow test looks for certain markers (proteins and hormones) on a sample of fluid, to give a positive or negative result. There are many different types of lateral flow tests - you may be familiar with a home pregnancy test or the quick COVID-19 test, both of which are rapid lateral flow tests.

The COVID-19 self-test can be ordered for free from The Centers for Disease Control and Prevention (CDC) encourages people that think they may have been exposed, or have symptoms, or will be meeting anyone who is vulnerable, or going to events or crowded places to be tested. This is designed to catch those without symptoms and prevent spread.

Is it still free?

As of December 2022, COVID-19 self-tests are still free in the US. Frontline healthcare workers or social workers may also be offered more specific tests, such as the polymerase chain reaction test (PCR).

Once tests are no longer free, you may still wish for the reassurance of negative lateral flow tests, especially if you have vulnerable people in your life, so they are available to buy from pharmacies and certain retailers.

If you have tested positive for COVID-19, re-testing is no longer required to end self-isolation. Isolation time depends on whether or not you had symptoms and if so, how severe they were. Please follow the guidelines on

How does it work?

A lateral flow test for COVID-19 has been developed which detects a protein (known as an antigen) that the body produces while fighting a current COVID-19 infection. The test cannot tell you if you have had COVID-19 in the past. Taking 20 to 30 minutes to get a result, a lateral flow test tends to be much quicker than a COVID-19 PCR test, where the samples must be sent off to a laboratory.

At the start of the COVID pandemic, lateral flow tests were thought to be significantly less accurate than PCR tests, but studies have found that when used correctly, they are around 80% effective at detecting any active COVID-19 infection.

Around a quarter of people who have COVID-19 don’t get any symptoms, so many people felt reassured with regular testing or if visiting elderly or vulnerable relatives or meeting lots of people.

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What happens in the test?

Testing is done by using a clean sterile swab (a thin plastic stick with a soft end, like a cotton bud) to collect secretions from the inside of your nose. You need to twirl the swab around for 5 seconds in each nostril. This can be uncomfortable and make your eyes water.

The swab then goes into a test tube containing some fluid where you will twist and press the swab against the side to release the secretions into the fluid. If you are doing the test for yourself, you will then put a few drops of this fluid onto the lateral flow device. After waiting a specified number of minutes, you are then able to read the results from your device.

Devices differ, but usually, two lines means a positive result, one line means a negative result (or occasionally an invalid test). Instructions may vary slightly with different testing kits, so remember to always read the label and check the expiration date.

Am I fit for work if I have a positive lateral flow test?

The CDC recommends to self-isolate if you know or suspect you have COVID-19, and to stay home for at least 5 days. The responsibility is with you to reduce the spread of infection by avoiding others and staying home. Your employer may have clear rules, but this relies on you to declare you have symptoms or have had a positive test.

Your co-workers may not thank you for turning up, and neither will friends and family, but we are all learning to live with the virus now, rather than to completely avoid it, so our attitudes to risk are changing with time.

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This article has been written by UK-based doctors and pharmacists, so some advice may not apply to US users and some suggested treatments may not be available. For more information, please see our T&Cs.
Dr Karen Martin
Reviewed by Dr Karen Martin
Reviewed on 19.10.2023
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