The COVID-19 pandemic caused by the novel coronavirus (SARS-CoV-2) has been posing a severe threat to human life and health since its discovery in December 2019. Testing is essential for the control and management of this pandemic worldwide. Numerous research studies have developed rapid COVID-19 detecting test kits to facilitate easy and fast diagnosis. They deliver a simple, cost-effective solution that gives results within half an hour. This can help restrict the affected individuals from spreading the disease to unaffected people.

What Is a Lateral Flow Test?

COVID-19 lateral flow tests (rapid diagnostic tests) help to test the virus that causes the infection quickly. Rapid diagnostic tests retrieve samples from the nose, throat to detect the viral proteins (antigen) related to the COVID-19 infection. If the viral proteins are present, they will show up as a colored line, similar to a positive pregnancy test. The results are delivered within 15 to 30 minutes.

When Should an Individual Go For a Lateral Flow Test ?

A lateral flow test (LFT) for COVID-19 is recommended for everyone above 11 years of age. They cannot get immunized by vaccine due to their age or health condition.
Lateral flow tests are done in asymptomatic patients with coronavirus symptoms.
It can also be used on a regular basis.
If attending a social event/ surrounding in a massive crowd.
LFT is highly recommended to avail before visiting patients who are at higher risk for severe illness.

The lateral flow test kit is designed to be used at home. There is no requirement to run the tests in a laboratory or with any outside healthcare facilities. However, speed and convenience come at the expense of accuracy. Care should be taken in the interpretation and communication of results.

How Does a Lateral Flow Test Work?

This test uses immunoassay technology that detects a specific chemical in a solution using antigen-antibody reactions. It has a nitrocellulose membrane, colored nanoparticles, and antibodies to produce results. When a sample is added, the sample will flow along with the test device through a conjugate pad (stores conjugate labels and antibodies) into the nitrocellulose membrane and then through the absorbent pad, which absorbs the excess samples.

The two types of lateral flow tests are:

Sandwich Assays: A positive test is represented by a colored line.

Competitive Assays: A positive test is represented by the absence of a colored line.

How Accurate Is a Lateral Flow Test?

The accuracy of any diagnostic test should consider sensitivity and specificity. Sensitivity means correctly identifying those with the disease, and specificity determines those who do not have the condition. The WHO recommends that rapid diagnostic tests for SARS-CoV-2 have a minimum sensitivity of 70 % and a specificity of at least 97%. Independent tests have found one such test by Biosensor. PCR tests are more reliable than a rapid lateral flow test. However, the high specificity of a lateral flow test helps confirm COVID-19 presence in the body accurately.

What Is the Difference Between a Rapid Test and a PCR Test?

PCR tests detect the virus’s genetic material in a given sample as well as it is accurate, whereas rapid tests detect the proteins from the virus. Lateral flow tests cannot distinguish between infected people who are infectious and those who are no longer transmitting the virus.

What Is Whole Population Screening?

Countries like Slovakia and the UK use lateral flow tests to screen the whole population using lateral flow tests. The British government has been using the Innova SARS-CoV-2 antigen rapid qualitative test in Liverpool, which has high spread rates, to identify the infected people. It is done in the hope of finding infected but asymptomatic patients and quarantining them to reduce transmission of the virus.

How to Interpret the Test Results?

When there is a higher risk of COVID-19 infection, positive lateral flow tests are a reliable indicator of the present disease in the patient. The ability of the LFT test to detect the virus is about 40 percent to 60 percent, according to a study in Liverpool. The developments in the device are promising and should match the sensitivity of a PCR test. Some countries, like the UK, have declared that a person who tests positive for COVID-19 on a lateral flow test has to isolate themselves, as there is no need to confirm with a PCR (polymerase chain reaction) test. When there is a rapid test result that is positive, the affected person has to isolate themselves. Reporting a result is also important, even if it is negative or void within 24 hours of getting it. This helps track the spread of COVID-19.

What Are the Advantages and Disadvantages of a Lateral Flow Test?

Advantages include-

Low cost
Ease of manufacture.
Easy to use
Long shelf life, no need for refrigeration.
High potential for commercialization.
Results are obtained in a short time.
Easily scalable in a mass population.

Disadvantages include-

Improper or reduced sample volume may affect the results.
Analysis time depends upon the nature of the sample. For example-viscosity.
Good antibody preparation is needed.
They are not confirmatory if tested negative.
Obstruction of pores due to matrix components in the test.

Is a COVID Antigen Test the Same as a Lateral Flow Test?

No, there are differences among the two of them. Lateral flow antigen tests are a type of quick turnaround virus test that can process COVID-19 samples on the spot and do not require any laboratory equipment to do so. These tests are a type of antigen test that utilizes a paper-based device to identify the presence of antigens in a sample. The majority of them generate results that can be understood in less than half an hour. As a result of this, they are capable of being carried out either in a laboratory or in a point of care setting.

Antigen tests are used to determine whether or not the SARS-CoV-2 virus, which is responsible for COVID-19, possesses certain proteins (antigens) on its surface. These tests are intended to deliver findings quickly and are typically utilized for testing at the point-of-care setting.

Conclusion

The World Health Organization (WHO) and other international organizations have recommended individual testing, mass population testing, and subsequent contact tracing to stop the chain of transmission of the COVID-19 virus. Hence, to control the transmission of the virus, there is an urgent need for large-scale, accurate, affordable, and rapid diagnostic testing assays. Advanced research should focus on developing a testing kit that is accurate in diagnosing the infection. The compact and easy-to-use lateral flow devices require no specialist training or equipment and are suitable for mass testing.