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Details of the different types of tests that can be done to detect and diagnose SARS-CoV-2 virus that causes the disease COVID-19 Leading to the coronavirus pandemic

By
Dr. B. J. C. Perera

Specialist Consultant Paediatrician

There are heaps of different ideas, veiled innuendos, public inquiries, all kinds of varied recommendations and countless queries about the different types of tests that can be done to detect and diagnose SARS-CoV-2 virus that causes the disease COVID-19, the coronavirus pandemic. It is a deadly disease that is relentlessly sweeping through all areas of the planet earth.

Some of these enquiries regarding the tests seek information while some others are rather mischievously designed to find fault with someone or the other or to question as to why this test or that test is not being used in our country. It is obvious, especially from media reports and even social media pontifications that many persons of the lay-public ask numerous questions as to why this test or that test is either done or not done. This article is written in good faith to provide some scientific state-of-the-art information for digestion by the general public on the current status of these tests. It is hoped that it would clear the air, at least a little bit.

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The very first of these tests for the diagnosis of COVID-19, and definitely the best known, is the RT-PCR test. This acronym stands for the scientific name of Real Time Reverse Transcriptase Polymerase Chain Reaction test. As the name suggests, RT-PCR is a technique used to monitor the progress of a Reverse Transcriptase Polymerase Chain Reaction in Real Time. It is based on the detection and quantification of relatively small amounts of the PCR product such as deoxyribonucleic acid or DNA, ribonucleic acid or RNA, and complementary DNA or cDNA which is double stranded DNA synthesized from single-stranded RNA. In very simplified terms DNA is at the very core of genetic material while RNA is a molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and DNA are nucleic acids, and, along with lipids, proteins and carbohydrates, constitute the major macromolecules essential for all known forms of life. Viruses contain either specific DNA or characteristic RNA. All coronaviruses are RNA viruses. In very simple terms, the RT- PCR is a test which amplifies the nucleic acids. It is of course not necessary for the general public to understand the complicated details of how exactly the test is performed. It should be left to the experts.

The test RT-PCR is a relatively rapid, convenient, sensitive and reliable method for virus detection. The most important thing for people to understand is that in COVID-19, it detects the presence of the virus itself. It is sensitive and precise for the detection of even small amounts of the virus. It is performed on nasopharyngeal swabs, oropharyngeal swabs, sputum, washings from the airways of the lungs, faeces and other test ingredients. These materials have to be either processed immediately or transported in viral transport media and immersed in ice during transport. For the test to be positive, the material to be evaluated should contain the virus and therefore it is important to realise that their yield could vary according to the sample that is tested, the stage of the disease and several other variables as well as some confounding factors. Currently the RT-PCR is the ‘gold standard’ for the definitive diagnosis of COVID-19. It is also important to understand and even stress that even those without major symptoms may be positive for the presence of the virus or the virus may still be present even after apparent recovery from the disease. Such individuals could test positive for the virus. These considerations have important implications with regard to the potential spread of the causative organism to other human beings and even to animals. The veracity and reliability of the test depends on scrupulous attention to detail on the part of those who collect the samples, those who transport the samples, those who receive and prepare the samples for testing, those who actually do the testing and those who interpret the results. So far it is to the eternal credit of all these heaps of fantastic personnel who have put their collective shoulder to the wheel, so that the machinery is made to turn nicely without any major technical setbacks.

The next test that is generally discussed is the test for antibodies. These could measure either Immunoglobulim M (IgM) or Immunoglobulin G (IgG), which are the specific antibodies against the incriminated coronavirus in question. It is crucial to understand that these tests DO NOT detect the actual presence of the virus. They only detect the antibodies produced by the defence mechanisms of the body in its fight against the virus. These antibodies are detectable and measurable in the blood of the patient. IgM antibodies are the ones that are produced by the body as a reasonably rapid reaction to the virus. The IgG antibodies are ones that are produced as a sustained response to the virus, leading to their persistence in the blood for a longer time. In all these considerations, it is crucial remember that as a well-known phenomenon, all antibodies necessarily take time to be produced by the human body in detectable levels to be noticeable in the blood. Although there is no hard and fast rule, it generally takes some time, sometimes up to one to two weeks for them to be positive. Therefore it is generally recommended that these tests should not be used on their own alone as diagnostic tools.

The production of these antibodies may also vary with age, nutritional status of the individual, immune capabilities of the body and the actual viral load. It is also theoretically possible that in very severe infections with extremely heavy viral loads, the antibodies may bind to the antigens of the virus in ever larger quantities so that sufficient amounts may not be left in the blood stream for them to be detectable. These antibodies generally indicate past exposure to SARS-CoV-2. Their real usefulness is in detecting susceptible individuals who are negative for these specific antibodies and at risk as well as identifying individuals who may have antibodies that could neutralise the virus and thereby be immune to further infections by the virus. They may also be used as methods to assess contacts as well as in epidemiological surveillance to detect the immune status of populations. It needs to be understood that antibody tests do have an important role to play in a holistic approach to this pandemic. More scientific research is required to see whether some of these antibodies are truly neutralising in their action or whether there are some of them that could enhance the activity of the virus, if and when there is a second infection. It might.., just might, even be similar to what we have seen in, and learnt from, dengue.

The last of the tests that are worth considering are the antigen detection tests. They help to detect, identify and measure the components of the virus that act as antigens to arouse and propagate an immunological defence reaction by the body. Antigens are various components of a foreign substance that are capable of stimulating the protective mechanisms of the body to produce antibodies. Therefore, the presence of such antigens is indirect evidence of the presence of the virus in the body. These antigens need to be very specific and sensitive for the unique structure and products of the virus itself. There are many methodological requirements that are necessary, some being quite a bit different from other tests, for the useful performance of these antigen tests. Several of these tests are in their early stages of development although many claims, some quite pre-emptive, are made for their usefulness.

These investigations are generally considered to be rapid tests that are easily performed on different materials from the body and the results would be available in a very short time. The great advantage is that they could be easily and rapidly performed at point of care without recourse to very sophisticated equipment. If these antigen tests can be perfected to have a high degree of specificity and sensitivity, they would be a very valuable adjunct and a most helpful agent in the diagnosis of this dreaded disease. The need of the hour is a well-designed research study to evaluate any given antigen test against the RT-PCR tests. If such scientific data hold the antigen tests on par with the RT-PCR, then their utility value would be akin to that of the NS1 antigen test in dengue. As a bonus, some of these rapid antigen tests are cheaper than the RT-PCR tests.

The doctors, researchers and scientists, here and abroad, are working very hard to assess and determine the real place for all these tests in the diagnosis and general management of the disease COVID-19. These dedicated and magnificent personnel are those who have put their dedication to their patients before even their own self-preservation. There is quite a way to go before delineating the exact place for some of these tests. As has been said, over and over, again and again, SARS-CoV-2 is a new, fresh or novel virus. All of us are learning on the go, as we traverse the many intricate pathways of the disease. What we should guard against are ‘knee-jerk reactions’ to prematurely make sweeping statements regarding these tests. Scores of very many medical scientists and clinicians are working day and night, even burning the midnight oil, to try and unravel the mysteries and vagaries of this virus that is most definitely a very real threat to humanity. Masses of data have to be gathered together, collated, analysed and compared. Then, and perhaps only then, would it be possible to arrive at definite, worthwhile and tangible conclusions. Now is definitely not the time for frivolous assumptions, blasé pronouncements, irresponsible declarations and even selfish actions to feather one’s own nest, in dealing with an enemy that is a tiny particle that has the capability to cause absolute mayhem and chaos in our little pearl of the Indian Ocean.

Finally, this is a fervent appeal to all the people in our beloved Motherland. All that the general public could do, and should do, would be to place their implicit trust in those who are working in our heath, scientific and academic communities towards the unified and determined goal of defeating this little virus that has sprung up from nowhere to herald hitherto unanticipated misery. We do not have to look far and wide, not even outside the shores of our emerald isle, to see what needs to be done. Some of the most brilliant and exquisitely capable minds are at work in our own country. It is left for all of us to let them make the vitally important decisions, which I am quite sure will ultimately end in a decisive and gallant victory against a relentless foe, which is SARS-CoV-2.

Courtesy:The Island