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COVID-19 Testing

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COVID-19 Testing

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Read this article to get an insight into the methods and protocols of COVID-19 testing.

Medically reviewed by

Dr. Sugreev Singh

Published At November 6, 2020
Reviewed AtApril 13, 2024

Introduction:

Rapid testing and vaccinations play a crucial role in breaking the transmission chain of coronavirus. Earlier, only polymerase chain reaction (PCR) and antibody testing were available. Now, there are several tests to detect both current and past infections. One such evolution is the development of a self-testing COVID-19 kit.

The Importance of COVID-19 Testing:

Ideally, during any infectious disease outbreak, public health officials begin testing for it early. This leads to the quick identification of cases, prompt treatment, and immediate isolation to prevent spread. Testing also helps in the early identification of people who came in contact with the infected people to prevent unconscious spread.

A lack of early testing has resulted in a rapid rise in hospitalizations, overburdening the healthcare system. In countries like South Korea and China, as tests were readily available when the first few cases were reported, they managed to drastically lower the death rate compared to other countries, such as the United Kingdom (UK) and the United States of America (USA).

Apart from diagnosing an active COVID-19 infection, the other important test is the one that determines the previous COVID-19 infection. When we get infected with a virus, our immune system fights the virus and protects us by producing antibodies. These antibodies can be detected with the help of blood tests. Even though the individual might not be infectious any longer, the information about past infections can be extremely valuable. Information about immunity to the new coronavirus can be obtained from this. Also, plasma from such recovered patients can be used to treat others with an active infection which is called convalescent plasma therapy.

Types of COVID-19 Testing

There are two types of tests available for COVID-19 testing, which include diagnostic tests and antibody tests. Antigen and molecular tests are the two types of diagnostic tests that help in detecting a current infection, while antibody tests detect a past disease.

1) Molecular Tests or RT-PCR Testing:

Presently, the majority of COVID-19 reports are coming from RT-PCR (reverse transcription-polymerase chain reaction), and it is the gold-standard test for COVID-19. RT-PCR first converts viral RNA (ribonucleic acid) into DNA (deoxyribonucleic acid), then amplifies that DNA. PCR (polymerase chain reaction) amplifies or replicates a small segment of the DNA several thousands of times, making it easy to be detected. As SARS-CoV-2 is an RNA virus that contains RNA, RT-PCR can help detect them. This test requires a few hours. The detection of viral RNA is only possible when the virus is present in the body, and someone is actively infected. Viral RNA is present in the body before antibodies or signs and symptoms develop. As a result, this test helps in diagnosis much early.

Sample Collection:

The likelihood of this test detecting the virus depends on the collection method and the time passed since the infection. Throat swabs are only recommended in the first week, as the virus moves deeper into the respiratory tract, multiplies in the lungs, and abandons the throat. During the second week, sputum collection is preferred. The samples can be obtained by throat swabs, nasopharyngeal swabs, sputum, or saliva. Nasal and throat swabs are 63% sensitive to RT-PCR, the pharyngeal swab is 32%, and the sputum is almost 75% sensitive.

Advantages:

PCR is beneficial when it comes to identifying individuals early in the course of infection. Such individuals can be isolated, and their contacts (people they came in contact with) can be quarantined too. It helps in breaking the transmission chain.

Limitations:

RT-PCR can be labor-intensive, and as it is an extensive process, errors can happen anywhere from sampling to analysis. 30% of the time, the reports can be false-negative.

2) Rapid Antigen Test:

The part of the virus that makes the body produce antibodies is called an antigen. SARS-CoV-2 antigen test looks for antigen proteins in the virus’s surface spikes. These antigens can be detected before the onset of symptoms, but this test is less sensitive than the PCR test. But, as the PCR test takes up so much time and is expensive, the antigen test is the way to scale up testing to a much greater level.

Sample Collection:

Here, samples are collected through nasopharyngeal swabs or saliva. The collected sample is then exposed to strips that contain artificial antibodies. The antigen present in the sample will bind to the coronavirus antigens on the strip and give a visual result.

Advantages:

This test is simple to do and takes less than 30 minutes. No expensive equipment or training is required and it does not require a visit to the laboratory. This test does not require deeper swab insertion; taking samples from the nares (openings of the nasal cavity) is adequate. In October 2021, the FDA made it a point to make the rapid test kits available over the counters so that identifying the infection is more effortless and facilitates timely isolation, thereby limiting the spread. Individuals can purchase rapid test kits to initially diagnose Covid-19

Limitations:

Throat and nasal swabs of respiratory viruses usually lack detectable viral antigen. This is more commonly seen in asymptomatic patients, as they have little to no nasal discharge. As the viral antigen is not replicated in antigen testing, the available antigen might be too little to get detected and might show false-negative results.

As the antigen test is only reliable if the viral load is high in the body, various doctors do not recommend getting it. At the same time, others argue that people with high viral loads are highly infectious, and by mass screening, such individuals can be identified. Also, in august 2021, a query arose on the test sensitivity after vaccination, if it will experience a fall due to the reduction in viral load. It is still in research in the U.S.

3) Antibody Tests:

This test detects the antibodies produced by our body to the viral antigen. Serology or blood tests can detect such antibodies. Antibody tests might not tell if the person has an active infection, but they can be used to assess the percentage of a population that has already been infected. A positive antibody test implies that antibodies are present either from a previous infection or from vaccination. It is also unclear if mild or asymptomatic patients produce sufficient detectable antibodies. The types of antibodies test that can be used to identify antibodies against SARS-CoV-2 are-

  • Rapid diagnostic test (RDT).

  • Enzyme-linked immunosorbent assay (ELISA).

  • Neutralization assay.

  • Chemiluminescent immunoassay.

Antibody testing will help identify the number of people in a population who are immune to the virus. Such immunity will stop frequent outbreaks of the new Coronavirus within the population. This is called herd immunity. In case someone gets infected, the virus will not be able to spread to others as long as others are immune.

Self-Testing COVID-19 Kit:

On 17th November 2020, the U.S. Food and Drug Administration (FDA) issued a EUA (emergency use authorization) for a rapid COVID-19 self-testing kit. This kit is called Lucira COVID-19 All-In-One Test Kit, a single-use test that can detect the SARS-CoV-2 virus responsible for causing COVID-19. People can use this kit to test for COVID-19 by self-collected nasal swab samples. This kit can also be used in hospitals, clinics, and emergency rooms if a healthcare provider collects the sample. These self-test kits can be used by self (14 years or above) or for kids ( two year and above) under the supervision of adults.

The nasal swab sample has to be swirled in a vial placed in the test unit. In about 30 minutes, the test unit's light-up display shows whether the person is positive or negative for the SARS-CoV-2 virus.

If you followed the instructions correctly and your test report shows negative results, you do not have an infection. However, it is advisable to get serial testing done as mentioned by the manufacturer to prevent the chance of the spread of the virus. If you get a positive report, immediate medical intervention is needed by a healthcare professional. Also, you should make sure to follow the necessary guidelines to prevent the spread of the virus.

Currently available over-the-counter at-home COVID tests are as follows-

  • Abbott Diagnostics Scarborough, Inc.- BinaxNOW COVID-19 Ag Card Home Test.
  • Abbott Diagnostics Scarborough, Inc.- BinaxNOW COVID-19 Antigen Self Test.
  • Access Bio, Inc.- CareStart COVID-19 Antigen Home Test.
  • ACON Laboratories, Inc.- Flowflex COVID-19 Antigen Home Test.
  • Becton, Dickinson and Company (BD)- BD Veritor At-Home COVID-19 Test.
  • Celltrion USA, Inc.- Celltrion DiaTrust COVID-19 Ag Home Test.
  • Cue Health Inc.- Cue COVID-19 Test for Home and Over The Counter (OTC) Use.
  • Detect, Inc.- Detect Covid-19 Test.
  • Ellume Limited- Ellume COVID-19 Home Test.
  • iHealth Labs, Inc.- iHealth COVID-19 Antigen Rapid Test.
  • InBios International Inc.- SCoV-2 Ag Detect Rapid Self-Test.
  • Lucira Health, Inc- Lucira CHECK-IT COVID-19 Test Kit.
  • Maxim Biomedical, Inc.- MaximBio ClearDetect COVID-19 Antigen Home Test
  • OraSure Technologies, Inc.- InteliSwab COVID-19 Rapid Test.
  • OSANG LLC- OHC COVID-19 Antigen Self Test.
  • PHASE Scientific International, Ltd.- INDICAID COVID-19 Rapid Antigen At-Home Test.
  • Quidel Corporation- QuickVue At-Home OTC COVID-19 Test.
  • SD Biosensor, Inc.- Pilot COVID-19 At-Home Test.
  • Siemens Healthineer- CLINITEST Rapid COVID-19 Antigen Self-Test.
  • Xiamen Boson Biotech Co., Ltd.- Rapid SARS-CoV-2 Antigen Test Card.

Saliva Test:

Andrew Books developed the saliva test in which, instead of the nasal swab or throat swab, a saliva sample was taken to diagnose COVID-19. These tests provided more consistent and accurate results. Even individuals with mild infections who tested false-negative for nasal swabs showed positive reports with a saliva test. Saliva tests reduce the risk of exposure to the medical professional taking the test because it does not produce sneezing or coughing. Some home tests use saliva to determine the presence of COVID-19 infection.

Other Tests:

In April 2022, FDA gave emergency use authorization (EUA) to use SARS-CoV-2 diagnostic tests that analyze breath samples. One such example is InspectIR COVID-19 Breathalyzer. Exhaled breath samples from people aged 18 and above with or without symptoms or other epidemiological reasons to suspect COVID-19 were found to contain five volatile organic compounds (VOCs) from the ketone and aldehyde families linked to SARS-CoV-2 infection. Only authorized settings can utilise this test in an emergency.

Who Should Take the Test for COVID-19?

1. People who have symptoms of COVID-19.

2. Individuals who have come in contact with COVID-19 infected people should take their tests in the following ways:

  • Fully vaccinated people should take their test five to seven days after exposure to the virus.
  • Partially vaccinated people should get tested immediately after contact. If tested negative, serial testing after fve to seven days should be done.

3. Unvaccinated people who have participated in activities with an increased risk of disease contraction.

4. Individuals who have been asked to get tested.

Conclusion:

Testing is a significant tool to reduce the control of viruses. More testing is needed to identify who is infected and who needs to be isolated. Countries like the USA, UK, and France have increased their testing capacities. Any form of testing is vital and will provide more information to tackle this pandemic.

Frequently Asked Questions

1.

What Distinguishes PCR From a Rapid Test?

The rapid test tends to be more accurate when the infection starts, as at that time, the body has the highest virus concentrations and is less sensitive than the RT PCR test. However, validating the results with an RT PCR test is always advised, even if the findings come back quickly.

2.

How Soon Do PCR Findings Appear?

The test results should be available to the person 24 hours after the sample is collected. Still, occasionally it may take a few days, depending on how quickly the sample is transported to the laboratory.

3.

Which Test—PCR or Antigen—Is More Accurate?

If a patient has symptoms or has been recognized as having close contact with someone who tested positive, PCR tests should be conducted to determine whether the person is infected. Compared to an antigen test, PCR tests detect considerably lower virus concentrations and identify whether the person has contracted it.

4.

How Do Antigen Swab Tests Work?

Specific proteins in the virus are found using the COVID-19 assay. Antigen tests can provide answers in only a few minutes using a nasal swab to collect fluid samples. Some might be taken to a lab for examination. A positive antigen test result is considered accurate when procedures are faithfully followed.

5.

What Kind of COVID Test Is Ideal?

Depending on the results of the person's antibody or antigen test, the test, which is the most precise of the three tests, is RT-PCR and usually does not require additional runs.

6.

Is Rapid Test a Viral Test?

Genetic material is termed RNA from the virus using molecular tests like the polymerase chain reaction (PCR) and other nucleic acid amplification tests (NAATs). Antigen tests, often known as rapid tests or, for some, at-home or self-tests, are used to identify the virus' antigens, which are proteins.

7.

Is an Antigen Test a Rapid Test?

For rapid PCR tests to be effective, SARS-CoV-2 virus genetic material must be found. On the other hand, antigen assays search for certain proteins on the cell's surface. Because of this, PCR testing is more precise than antigen tests. 

8.

How Are Antigen Tests Conducted?

Currently, saliva, nose swabs, or nasopharyngeal specimens deposited directly into the assay's extraction buffer or reagent may be used for antigen testing. In addition, point-of-care, laboratory-based, and self-tests are currently permitted antigen tests.

9.

How Long Does It Take To Get the Results of a Swab Test?

Coronavirus testing comes in three primary categories: PCR, antigen, and antibody. Rapid antigen testing that can produce results in about 15 minutes has been developed. Results from RT-PCR are normally available 24 to 48 hours after receiving the sample.

10.

Is a Lateral Flow Test Equivalent to a Rapid Antigen Test?

Rapid turnaround virus testing, known as lateral flow antigen tests, can handle COVID-19 samples on-site without lab apparatus. The majority delivers clear results in less than thirty minutes.

11.

Is Having COVID While Testing Negative Possible?

If the test is negative, it is improbable that one has COVID-19 at the time of the test. The nasal swab sample did not contain any antigens, although it is possible that the test resulted in a false negative.

12.

How Long Does the COVID Virus Last?

A mild case of COVID-19 symptoms will last for around two weeks. However, it can take months if one has a more serious condition or additional health issues. When a person has long-COVID, their symptoms can endure for four weeks or longer and last after recovery.

13.

How to Get a PCR Test?

 
A medical professional will use a swab to collect a sample from the throat and nose. Although it could seem unpleasant, there will not be any pain. Youngsters under thirteen need to provide a nasal swab sample. The sample will then be sent to a lab for analysis.

14.

Is a Molecular Test a Rapid Test?

Rapid antigen tests, which seek protein markers on the surface of the virus, are one type of diagnostic test. In addition, molecular assays, including PCR, LAMP, and CRISPR, check for viral genetic material specific to SARS-CoV-2.
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Dr. Sugreev Singh
Dr. Sugreev Singh

Internal Medicine

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severe acute respiratory syndromecovid-19
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