What is a Lateral Flow Test and how does it work?

05 October, 2021  |  Camran Khan

What is a Lateral Flow Test and how does it work?

What is a Lateral Flow Test?

The Lateral Flow Test looks for viral proteins (antigens) of the COVID-19 virus in the swab sample. It’s a test that has been widely used before for different purposes owing to its ability to analyze a wide range of biological samples to test for a particular substance and provide a quantitative value for it. Although it’s limited to nasal swabs for COVID-19, in principle it can test other bodily fluids as well, like saliva, sweat, urine, blood serum, plasma, and blood. The benefit of Lateral Flow Testing over most available testing methods is that it can be performed with relative ease, costs a lot less, and usually presents the results within minutes. 

New testing rules for travellers

The UK government recently announced an overhaul to the testing rules and requirements for people planning to travel to the UK. The traffic lights system has changed and new rules have come into effect from the 4th of October, 2021. As per the new rules, fully vaccinated international arrivals to the UK from countries not on the red list will need to take a Lateral Flow Test before arrival. A Day-2 RT-PCR test will still need to be taken upon arrival, but that is set to be replaced with the Lateral Flow Test by the end of October. 

The acceptance of the pre-departure Lateral Flow Test in the UK adds to a growing list of countries that are doing the same. Travellers from the UK can already obtain a Fit to Fly certificate through a Lateral Flow Test and travel to countries like the United States, Germany, France and more. 

How to take the Lateral Flow Test

You can buy the Lateral Flow Test from IQ doctor — an accredited test provider with quick delivery of kits and turnaround time of results. To take the test, you are to follow the Lateral Flow Test instructions that come with the kit. These instructions include the following steps:

  • Make sure you haven’t had anything to eat or drink in the last 30 minutes.

  • Wash your hands and clean the surface where you will take the test.

  • Take the test within 30 minutes of removing it from the packaging.

  • Open the pouch and take out the cassette. The cassette will have a result window and a specimen well.

  • Remove the aluminium foil from the top of the extraction buffer tube.

  • Insert the tube into the hole in the kit box.

  • Open the swab packaging and take out the swab. Make sure that you hold it at the stick end and not the side with the fabric tip.

  • Insert the fabric tip of the swab into your nose. Slowly push it up to your nose until it is one to two centimetres in, or when you start feeling resistance. Make sure that the tip of the swab does not touch anything other than the inside of your nose.

  • Put the fabric tip of the swab in the fluid of the extraction tube. Mix it thoroughly.

  • Put two drops of fluid from the extraction tube onto the test cassette.

  • Leave the test cassette on a clean surface for 20-30 minutes. 

  • After 20-30 minutes, note the results. Interpret the results based on the instructional image that will be provided with the kit. 

Unlike most other testing services, IQ doctor provides added convenience in interpreting the results and getting any certification for travel. You will have the option to take a picture of the test cassette, Log in at the IQ Doctor website and upload the image. After reviewing the image, the IQ Doctor team will relay the results in quick time. 

What do the Lateral Flow Test results mean?


If your Lateral Flow Test result is inconclusive, you will need to retake the test. The inconclusive result could be due to not following the procedure correctly, having excess mucus in the nasal cavity, lack of inactivation solution in the cassette, contamination from external sources, or some other manual error.

You will need to repeat all steps using a new swab and test cassette and make sure to follow all the instructions in the correct order provided with the kit. You will also have to report your inconclusive result to the NHS.


If your Lateral Flow Test result is positive, you and your household will need to self-isolate immediately per Government guidelines. You will be required to report your test results to the NHS and book a confirmatory PCR test.

NHS Test and Trace will contact you, and you will have to enter ten full days of self-isolation. Your self-isolation period starts immediately from the time you begin to experience symptoms of COVID-19. If you don’t have any symptoms, your ten days will start when the test is taken.

For these ten days, you will be expected to not travel anywhere or meet anyone in person for the entire duration of these ten days. If your confirmatory PCR test is negative, and you are asymptomatic, and if no one in your household has symptoms or tested positive, you and others in your home would be allowed to stop self-isolating. 


If your Lateral Flow Test result is negative, your movement will not be restricted. However, you will still have to report your results to the NHS and continue following all other COVID-19 related Government guidance, including regular handwashing, social distancing and wearing face coverings, where required. 

Are Lateral Flow Tests an effective method for diagnosing COVID-19?

According to the 2020 Liverpool trials of Lateral Flow Tests, the speed and economy of Lateral Flow Tests come at the cost of their accuracy and sensitivity. The trials showed that Lateral Flow Tests have an average sensitivity rating between 88.75% and 99.17%, from a total sample of 20 million tests that were part of the trial. Therefore, Lateral Flow Testing can be noticeably less accurate than RT-PCR tests. The primary advantage Lateral Flow Tests had over RT-PCR tests was that they are effective at quickly testing a large number of people within a workplace or educational institute to detect highly infectious cases of COVID-19. This does not mean that Lateral Flow Tests should replace RT-PCR tests entirely, with some people warning that ending compulsory PCR testing will lead to dire problems within the near future, such as the spread of new COVID variants. The comparatively lower sensitivity rating of Lateral Flow Tests also means that it can be a particularly inaccurate test of COVID-19 for someone who is not showing any symptoms. The sensitivity rating drops even lower the longer someone has been infected with COVID-19.

Are there any potential drawbacks to ending mandatory PCR tests?

Some critics have warned of adverse outcomes due to the UK government no longer requiring travellers to get RT-PCR tests. With fully vaccinated travellers now being directed to instead pay for their Lateral Flow Testing, there is an increased chance of the LFT failing to detect some asymptomatic cases of COVID-19, which can increase the risk of new variants slipping through and spreading among the general population.

Once the Day 2 test is phased out by the end of October, travellers will be required to get an RT-PCR test done in case they get a negative on their Lateral Flow Test.

Lateral Flow Tests are an invaluable tool in the fight against COVID

The UK earlier undertook a pilot study to determine the viability of the Lateral Flow Test. The results were promising, and therefore, since 4th October, the rest of the country has followed suit and now uses the Lateral Flow Testing. The economy of scale offered by Lateral Flow Testing makes it a practical and scalable method for testing large numbers of people in a short time. The Lateral Flow Tests will also be effective at detecting most cases of asymptomatic infections. People who test positive on a Lateral Flow Test will know that they have to enter isolation to avoid infecting anyone else. While not perfect, Lateral Flow Tests are accessible to more people than PCR tests were in the past. The low cost and ease of use of Lateral Flow Tests make them the perfect first line testing method.

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