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How Lateral Flow Tests Identify Active COVID-19 Infections

The effects of COVID-19 on the affected persons have been a constant reminder that individuals must embrace testing. It is one of the most powerful strategies for mitigating the spread of the SARS-CoV-2 virus. Testing has to happen regularly, especially if you suspect you have had close contact with an infected person. When people get frequently tested, those who are found positive can easily self-isolate to prevent spreading the virus further. Apart from that, the people you were in contact with usually get notified to also test themselves. That way, it is possible to know the extent to which the virus had spread, making it easier to prevent it from further spreading. 


You can use lateral flow tests (LFTs) or go to a healthcare facility to get tested. Both options are effective. COVID self-tests give quicker results and are more convenient. Also, most people prefer LFTs for their simplicity and accessibility. Such attributes make the tests instrumental during mass screening efforts. So, how do lateral flow tests identify active COVID-19 infections? In this article, we delve into an in-depth discussion of self-testing.

Sample Collection 

It is important to note that COVID-19 is still getting people hospitalized, which explains why people need to test themselves regularly. In England, around 2600 people were hospitalized in the week between 2nd and 8th December 2023. Sample collection is the most crucial step in this process. Here is why. The reliability and accuracy of the tests heavily rely on how you have collected the samples. That implies that you can get false self-test results because samples are collected incorrectly. Here, you may use a nasal swab or a throat swab. Nasal swabs will require you to insert your swab into your nostril up to the back of the nasal cavity to collect your sample. If you choose to go for the throat swab, you will rub the swab against the back of your tonsils or throat. You will either need to rinse your mouth with water or blow your nose before the exercise. Collecting the samples during the early stages of the infection is effective. By then, the viral load is usually sufficient for detection.

Application of the Sample

You see, lateral flow tests have had a huge global impact in the war against COVID-19. If other people have learned how to take valid tests, you, too, are not an exception. Here, you introduce the sample to the test device. Before you apply your sample to the lateral flow test device, you must prepare it.  During the preparation stage, you mix the sample with the required reagents to ensure it is in an optimal state. That way, it can easily interact with the test components. When identifying the application area, you need to understand that the strip has three zones, each of which serves a specific purpose. You deposit the sample at the introduction zone, after which capillary action takes over.


Migration of the Sample

The sample then migrates to different zones of the strip. The design of the strip is what encourages the movement of the liquid. It has porous membranes with a network of capillaries that allow controlled movement. It flows to the detection zone, where it finds certain molecules, usually antibodies. These antibodies or various captured agents are supposed to selectively bind to the target viral components found in the sample. 

What Happens in the Detection Zone?

When your body detects a foreign substance, for instance, a virus, your immune system will produce antibodies. When it comes to lateral flow tests, those antibodies are strategically selected. They can also be engineered to bind to certain antigens. That aids in the detection of COVID-19. For instance, if you are planning to travel you need to carry out the test beforehand. So when trying to detect SARS-CoV-2, the molecules will interact with viral antigens like nucleocapsid proteins or spike proteins.  In the detection zone, there are mobilized viral antigens that assist in capturing the molecules. The immobilized antibodies and the target viral components go through selective bonding. 

Result Interpretation

It all begins at the control zone. The control zone is an important component created to perform as a built-in control measure. In other words, the control zone ensures the accuracy and reliability of the test. It captures the contents of the sample to come up with a control line. This is different from the detection zone. You get to see the results through the detection zone. Here, healthcare officials and individuals get to see visual cues to determine whether there is an infection. After putting the sample, you wait for 15 to 30 minutes. You need to examine the test strip, checking the presence or absence of visible lines. 


There is usually a specific binding of the viral antigen to the immobilized antibodies and antigens. It happens at the detection zone. The darkness of the line may vary, but that should not worry you. It is determined by how concentrated the detected viral material is. You also need to check the control line. If it is missing on the test strip, then there was a problem with the quality of the test strip or the procedure.


For you to declare the test positive, you must have seen two things. The control line on the control zone and a test line on the detection zone. On the other hand, if the test is negative, you will only see a control line. For invalid tests, the control line is usually not available. 


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