Lateral Flow Test Guide: How Do Lateral Flow Tests Work?

Lateral flow testing is now widely used to help us travel more conveniently and are quick, easy and hassle-free, giving you instant test results in under 30 minutes and are increasingly being accepted for travel around the world.

In this article, you will find all you need to know about Lateral Flow testing.

Introduction - What is a Lateral Flow Test?

A short video guide to Lateral Flow Testing

A Lateral Flow Test is a simple diagnostic device that is used to verify the presence of pathogens or biological agents in humans or animals. The most common type of Lateral Flow test is the pregnancy test.

A Lateral Flow Test is a simple diagnostic device that is used to verify the presence of pathogens or biological agents in humans or animals. The most common type of Lateral Flow test is the pregnancy test.

The Lateral Flow Tests (LFT) are popularly used across many different industries for testing such as pharmaceuticals, environmental testing, animal health and food testing. When the coronavirus broke out worldwide, the Covid-19 Lateral Flow device was introduced to the mass market as a preventative measure to control the spread of the Covid-19 virus.

The use of the Covid Lateral Flow Test involves taking a swab sample from the nose or throat, mixing the swab sample into the liquid in the tube and dropping them into the cassette disk. The result usually appears within 20 minutes. Due to the nature of use that is fairly easy and fast performing, the Lateral Flow Test can be used by both trained professionals and individuals in various settings. In fact, in the UK, the LFT was introduced for instant use at home and individuals are advised to take the test twice a week.

Common Names for Lateral Flow Tests

The Covid-19 Lateral Flow Tests have been called with many different names across various resources, such as:

  • LFT — an abbreviation for Lateral Flow Test
  • Lateral Flow Device or LFD
  • Lateral Flow Immunoassay or LFIA
  • Rapid Test
  • Antigen Test
  • Dipstick
  • Quick Test
  • Test Strip

The above names share the same meaning. However, do take note that the lateral flow or antigen test is not the same as the antibody test, which confirms if you have had the Covid-19 virus before or if you have been vaccinated for Covid-19. Click here if you would like to learn more about the difference between antigen and antibody tests.

How To Get The Lateral Flow Test

The lateral flow test (LFT) is readily available for free in the UK and is very easy to obtain in all of these places:

  • The NHS

You can get the lateral flow test or rapid antigen test for free and online from the NHS website. The test package comes in a pack of 7 and you are advised to take the tests twice a week, to help control the spread of the virus.

  • Pharmacy and community centre

In England, you can also obtain your free rapid tests from a pharmacy (i.e. local pharmacy, Boots, Superdrug) or community centres and libraries near you. When you collect from a pharmacy, you may collect 14 tests at once.

  • Private provider

If you are taking a test for travel purposes, you must not use the free NHS tests and you are required to purchase from private providers, who will issue a doctor-signed result and certificate. Please make sure that the company of your choice is government-listed.

How Does a Lateral Flow Test Work?

The covid lateral flow device (LFD) uses a technology called immunoassay, which is a biochemical test that detects the presence or absence of pathogens in living organisms.

The lateral flow immunoassay device usually contains an absorbent pad, nitrocellulose membrane and control line to detect if the test is working correctly, alongside other test lines. When a sample is added to the device, it will flow through the device onto the absorbent pad and within minutes, a result will appear to show if the pathogen is present or absent. When it comes to the Covid lateral flow test, two lines indicate the presence of coronavirus, which means that the individual is positively infected with Covid-19. On the other hand, one line indicates that the coronavirus is absent in the sample and the patient is tested negative from Covid-19.

Types of a Lateral Flow Test

The lateral flow immunoassay test can use two types of approaches: Sandwich or Competitive assay. They are both popular methods for a lateral flow device or LFD and they work in a similar way. The choice of this mechanism usually depends on the industry, sample type and market requirement.

  • Sandwich or Non-Competitive assay

The sandwich immunoassay is used for large molecular weight analytes that contain multiple antigenic sites. For the result, a coloured line indicates a positive test and the absence of a coloured line indicates a negative test. This format is not suitable for small molecular weight analytes. The most popular type of sandwich assay is the pregnancy test and Covid-19 lateral flow test.

  • Competitive Assay

The competitive immunoassay is used for small molecular weight analytes with single antigenic sites. Contrary to the sandwich assay, the absence of a coloured line points to a positive test and a negative test is represented by the presence of a coloured line. This format is not suitable for large molecular weight analytes. A popular use of the competitive assay is a specialised test for drugs and toxins.

Multiplexed Lateral Flow Assays

A multiplexed assay is a type of immunoassay that can simultaneously test and measure multiple analytes in a single test. Both, sandwich and competitive assays can be developed into a multiplexed assay, in the form of one or more lines on the lateral flow device. In the case of the LFT Covid test, it uses the sandwich immunoassay approach that includes one test line and one control line.

Advantages of the Multiplexed Lateral Flow Assay

The multiplexed method is a popular use of immunoassay across different industries, as it accommodates individuals to detect multiple targets in a single test rather than performing many single tests. Because of this ability, the multiplexed immunoassay allows us to maximise its use when the sample volume is small, saving cost and time by testing different targets simultaneously.

What is a Quantitative Rapid Lateral Flow Device

The traditional lateral flow test (LFT), often relies on a visual assessment of the test and qualitative-based assay, which, to a certain degree, may limit the objectivity and information output of the assays. With improvements in reagents, manufacturing process and reader technology, quantitative results can be achieved. To provide this quantitative information of the target in the sample, an additional reader is required to scan the lateral flow device (LFD).

How To Do a Rapid Lateral Flow Test

The rapid lateral flow test (LFT) is easy to use and suitable for home use. The LFT involves rolling a swab inside of each nostril. You should do this ten times per nostril to ensure a good quality sample. The swab is then placed into a liquid to allow the sample to dissolve in the liquid. This liquid is then dripped onto the device’s pad in the form of a house cassette, producing a reaction that gives a result. See the infographic below for a step by step visual on how to perform the LFT on yourself.

What To Do Before Doing a Rapid Lateral Flow Test

Before doing the rapid test at home, please make sure you:

  • Do not eat, drink or smoke 30 minutes before performing the test, as this may affect the result of your test.
  • Read the instructions and follow the step-by-step guide.
  • Start the test not more than 30 minutes after opening the test kit.
  • Check that the test is not broken or damaged.
  • Clean and sanitise the surface you are conducting the test.
  • Clean and sanitise your hand.

Step-by-step Guide on Performing the Lateral Flow Test

To perform the lateral flow test, here are the complete step-by-step procedures on how to perform the test.

Before performing the test:

  • Read the instruction manual carefully
  • Wash your hands thoroughly for 20 seconds with soap and water
  • Unpack and lay out all the kits on a clean surface
  • Put the tube filled with liquid in the tube holder
  • Blow your nose and make sure your nostrils airway are clear
  • Wash your hands again


Taking the swab:

  • Unpack the swab from the wrapper and find the soft, fabric tip
  • Insert the fabric tip of the swab in one nostril. Gently rotate the swab and push the swab until you feel a restriction. This is usually up to 2.5 cm from the edge of the nostril. Do not insert any deeper if you feel strong resistance or pain
  • Rotate the swab 5 times
  • Remove the swab and insert the same swab into the other nostril
  • Repeat the step


Completing the test:

  • Place the swab with the fabric tip into the tube
  • Rotate the swab (inside the tube) for 30 seconds
  • Pinch and squeeze the tube while rotating the swab for 5-6 times
  • Remove the swab from the tube and dispose of the swab safely
  • Attach the dropper tip on to the tube
  • Make sure the test kit is on a clean and flat surface
  • Gently squeeze the tube and place 4-5 drops onto the house cassette
  • Wait 10-20 minutes for the result to appear
  • Read your result. Provided below is the interpretation of the test results
  • When you are done, don’t forget to safely dispose of the test and wash your hands

Reporting your result:

      • It is important to report your test result:

    If you used the NHS test, you can report using the QR code and ID number on your test cassette, then report them online on


  • If you buy a lateral flow test from a private provider such as Medicspot, you can follow the instructions attached to your test kit and register them online on

What to do if you need help to do the test

If you need help, you can:

  • Check out our video (link to our near-future video) on how to perform the test.
  • Call the NHS on 119 to guide you through.
  • Do the test at a test site and ask for a trained helper to guide you.

What to do when you are doing the test on someone else

When you are performing the test on someone else, it is important that you:

      • Explain to them the steps
      • Remain calm
      • Make sure that the person remains calm
      • If necessary, get another person to help you
      • Stop doing the test if the person becomes uncomfortable and distressed
      • Make sure that your hands are washed and sanitised before performing the test

    If you are performing the test on a child, you can find out more details




So, how does it work?

Home Tests

Book in seconds

Select a day and time that suits you — then see a doctor on your phone or at a pharmacy.

Referral Letters

Speak to a doctor

Have a video consultation and be examined by one of our expert doctors.


Get back to feeling better

Whether it’s a diagnosis, personalised treatment plan or prescription — our doctors can help.

Our GPs are guided by a set of core values
Appointments from 13:30 today

Chat to a doctor at the click of a button