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COVID-19 Lateral Flow Test

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COVID-19 Lateral Flow Test

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COVID-19 lateral flow test is a rapid test to check if someone has a COVID-19 infection. To know more about this test, read the article below.

Written by

Dr. Sowmiya D

Medically reviewed by

Dr. C. Elanchezhian

Published At January 8, 2022
Reviewed AtJune 30, 2023

Origin of Coronavirus 2019

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-

  1. Low cost

  2. Ease of manufacture.

  3. Easy to use

  4. Long shelf life, no need for refrigeration.

  5. High potential for commercialization.

  6. Results are obtained in a short time.

  7. Easily scalable in a mass population.

Disadvantages include-

  1. Improper or reduced sample volume may affect the results.

  2. Analysis time depends upon the nature of the sample. For example-viscosity.

  3. Good antibody preparation is needed.

  4. They are not confirmatory if tested negative.

  5. 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.

Frequently Asked Questions

1.

What Is Meant by Lateral Flow COVID Tests?

Lateral flow tests are rapid turnaround virus tests that can detect novel coronaviruses (2019-nCoV) N protein antigen, which is obtained from the nasal swab sample. This reduces the need for the use of laboratory equipment. Understandable results can be derived in less than half an hour. This facilitates its use in a care setting. This method is not new and has been in use even before the COVID-19 pandemic. The kits used are portable, handy, and small, and less training is sufficient to carry out the test.

2.

Is a Rapid COVID Test Similar to a Lateral Flow Test?

A rapid COVID-19 test is indeed similar to a lateral flow test because rapid testing includes the use of lateral flow technology to identify proteins or antigens that exist in a person infected with the COVID-19 virus. Rapid antigen tests and lateral flow tests are the same, but these differ from COVID-19 PCR tests in that the samples collected are sent to the laboratory in case of COVID-19 PCR tests, and these are accurate. The PCR test can identify even lower levels of the virus and also detect previous COVID-19 infections.

3.

What Constitutes the Lateral Flow Test Kit?

The conjugated pad present in the lateral flow assay kit contains carbon, conjugated gold, or colored latex nanoparticles. Other labels comprise magnetic beads or colored polystyrene beads. Whatever the type of labels may be, they carry out the same function, that is, to create a three-way bond with the targets and antibodies so that the control and test lines are visible. The sample is collected from the nose alone or from both the nose and throat using a swab.

4.

Which Is the Reliable-PCR Test or the Lateral Flow Test?

The PCR test can confirm the diagnosis and is more reliable than the lateral flow test. The polymerase chain reaction (PCR) tests can detect the viral genetic material of the COVID-19 virus. PCR tests can be taken if a person has symptoms or has been in close contact with someone positive to know if the person is infected. The PCR test can identify even lower levels of the virus and also detect previous COVID-19 infections. Lateral flow tests are rapid tests, and there are chances of getting false positives or false negatives, especially in the early stages of the infection.

5.

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

Antigen tests are rapid tests and require sufficient viral antigens in the specimen for the antibodies on the test strip to induce a signal. The most precise COVID-19 test is the PCR test in which the reagents are used to convert the RNA into DNA to confirm if there is any infection in a person. Antigen tests merely detect the proteins present on the surface of the virus to detect the pathogen. The results from rapid tests are obtained in less than half an hour.

6.

How Is the Lateral Flow Test Carried Out?

A swab is used to collect samples from the back of the individual’s nose and throat. The swab is then inserted inside a tube containing a liquid, following which a small sample of this liquid is placed on a small absorbent pad provided within the disposable testing kit. The liquid is absorbed by the pad through capillary action until it comes in contact with the strip containing the antibodies specific to the SARS-CoV-2-virus antigen. A colored line indicates the presence of antigens, and hence, the result is positive.

7.

What Is Meant by the Lateral Flow Method?

Lateral flow tests are rapid turnaround virus tests that can detect novel coronaviruses (2019-nCoV) N protein antigens. A swab is used to collect samples from the back of the individual’s nose and throat. The swab is then inserted inside a tube containing a liquid, following which a small sample of this liquid is placed on a small absorbent pad provided within the disposable testing kit. The liquid is absorbed by the pad until it comes in contact with the strip containing the antibodies specific to the SARS-CoV-2-virus antigen. A colored line indicates the presence of antigens, and hence, the result is positive.

8.

Does the Lateral Flow Test Provide Accurate Results?

A study shows that lateral flow tests are more than 80% effective at identifying COVID-19 infection at any level and nearly 90 % effective at identifying those who are most infectious. A positive lateral test result can indicate an infection since the specificity and the capability of lateral flow tests to diagnose precisely uninfected persons are higher, and the chances of false positives are relatively rare.

9.

Are Rapid Tests Capable of Detecting Omicron?

An analysis shows that the rapid tests are slightly better in identifying the Omicron variants within 48 hours of being tested positive on a PCR test. They can probably detect the Omicron variant only when the viral load is high. The World Health Organization (WHO) has stated that the rapid antigen tests and the PCR test can identify Omicron and the previous variants.

10.

How to Test for Omicron?

The samples collected through swabs in a PCR test can be sent to the laboratory for analysis. A complete genetic analysis is needed for the confirmation of Omicron, which might take around 4-5 days. A close look at the genetic material obtained through testing can confirm the presence of Omicron in a person.  The World Health Organization (WHO) has stated that the rapid antigen tests and the PCR test can also identify Omicron and the previous variants.

11.

At What Intervals Should I Take a Lateral Flow Test?

Taking the lateral flow test twice a week is recommended. These tests should be taken with an interval of three to four days in between. It might be necessary to take the test before surgery or a procedure as suggested by the doctor. Those working at school, nursery, or college should undertake the test twice a week. People are advised to undertake the lateral flow test when they are more susceptible to catching or spreading COVID-19.

12.

When Can the Lateral Flow Test Results Be Expected?

Lateral flow tests are rapid turnaround virus tests that can detect novel coronaviruses (2019-nCoV) N protein antigen, which is obtained from the nasal swab sample. This reduces the need for the use of laboratory equipment. Understandable results can be derived in less than half an hour. The result is positive if two lines appear on the test. The results should not be read after 30 minutes.

13.

How to Know if the Result From the Lateral Flow Test Is Positive?

Lateral flow test reduces the need for the use of laboratory equipment. Understandable results can be derived in less than half an hour. The result is positive if two pink lines appear next to ‘C’ and ‘T’ on the test. Even faint lines indicate that the test is positive. The results should not be read after 30 minutes as it can lead to false positive results, and the test needs to be repeated.

14.

Will the COVID Vaccine Influence Lateral Flow Tests?

The COVID-19 vaccine will not influence the result of the lateral flow test. Since the body develops an immune response to vaccination, there are chances that the person may test positive on a few antibody tests. The protein produced following the entry of the mRNA or DNA following vaccination with the mRNA or vector vaccine is not identified by the rapid antigen or PCR tests.

15.

Is Antigen Test Accepted for Travel in India?

All arrivals entering India must upload a negative PCR test result not older than 72 hours in India’s Air Suvidha portal. Travelers who are fully vaccinated do not require pre-arrival testing. Some regions within India expect negative results from domestic travelers. Rapid tests are accepted if they are viral tests and meet the needed requirements under the Order.
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Dr. C. Elanchezhian
Dr. C. Elanchezhian

General Medicine

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