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What is a lateral flow test and how does it work?

The advent of COVID-19 has placed lateral flow tests in the spotlight. In reality, though, lateral flow tests have been around for a while, helping doctors and patients make quick yet reliable diagnoses for various diseases, leading to the right treatment plan.

But what really is a lateral flow test and how does it work? This article will help you understand what it is, so you’ll have more knowledge when you hear a doctor order lateral flow test for you or your loved ones.

What is a lateral flow test?

A lateral flow test can be caller a variety of names including lateral flow device, lateral flow assay, lateral flow immunoassay, or lateral flow immunochromatographic assay. There are also more common names such as rapid test, quick test, test strip, or something similar.

Lateral flow tests are diagnostic devices that can help confirm the presence (or the absence) of analytes such as contaminants or pathogens. Such analytes can be detected in a variety of matrices such as blood, saliva, urine, and tissue samples. They can also be used in checking out contaminants in water, milk, food, and fuel. 

There are many conditions for which a lateral flow test can be used and among the most common is the pregnancy test. Recently though, lateral flow tests have been placed in the forefront for quickly detecting SARS-CoV-2 which causes COVID-19.

What are the types of lateral flow tests?

Lateral flow tests can come in the form of a dipstick or a housed cassette, but they typically work in the same way. 

There are different types of lateral flow tests. They are typically categorized into two major types of assays: sandwich assay and competitive assay. A sandwich assay is one whose positive results are indicated by the presence of a colored line in the target or test line. A competitive assay is the opposite, where a positive result is indicated by the absence of a colored line. 

How does lateral flow test work?

Lateral flow tests make use of nitrocellulose membrane, labels (made of colored nanoparticles), and usually antibodies, in order to arrive at a result. 

Once a sample is added in a competitive assay, the sample will reach the nitrocellulose membrane. There is usually a control line (the first line in most lateral flow tests) which aims to confirm that the test is working. After that, the sample will flow through the target line (or test line) and if the target analyte is present, antibodies will bind to them. This will lead to the second line in most lateral flow tests. If the second line doesn’t show up, this means that the target analyte is not present.

Lateral flow test for COVID-19

As mentioned, the popularity of lateral flow tests have been renewed with COVID-19. Lateral flow tests for COVID-19 are more commonly referred to as rapid tests kits, and have been placed in huge demand as they have been made available to the general public in most parts of the world.

Rapid COVID-19 test kits usually make use of mucus obtained through a nose or throat swab. The sample is then dipped into a tube with a solution, and then placed into the test cartridge. Antibodies for SARS-CoV-2 will then recognize if the virus is present, showing a colored line in the test/target line.

Lateral flow tests have proven to be effective ways in detecting the presence of substances and pathogens, which help doctors design the right intervention. Quick, reliable, and affordable – these are characteristics which ensures that lateral flow tests will continue to be around, and will be developed to help detect emerging diseases and conditions in the future.