Tests for the new coronavirus: How they work

Posted onMarch 22, 2021

Testing for the new coronavirus in different countries and even cities is not the same: the policy adopted depends on at what stage of the outbreak a particular place is, as well as on the availability or lack of tests and on the priorities of the healthcare system. There are methods that detect the virus itself, and tests for antibodies to it; you can hear that it takes from several minutes to several days to get the result. We figure out how the tests work and whether you need to buy them yourself if you have no symptoms.

How Antibody Tests Work

During a coronavirus infection (visible or asymptomatic), the immune system reacts by producing antibodies – these are special proteins also called immunoglobulins; they are specific, that is, they approach this virus like a key to a lock. By determining their presence in the blood, you can find out if a person had this virus. It is important which antibodies the test detects – for example, type M immunoglobulins (IgM) appear on the seventh day, and disappear by the 21st; other antibodies, such as IgG, appear about two weeks after infection and remain in the blood for a long time, providing immunity from re-infection. Recovered people who have detected IgG to coronavirus can become plasma donors – it is used to treat COVIZ-19 patients.

Detecting not the virus itself, but the immune response to it, that is, the antibodies developed in a person, is a different approach to testing. The tests that are used for this are also cheaper and easier to work than PCR for detecting viral RNA. A drop of blood is needed for the analysis. Among the disadvantages is that such a test has a lower specificity, that is, it can more often give a false negative result. In addition, the production of antibodies in the body takes several days, so at an early stage after infection, the result may be negative, although the body has a virus.

When analyzing antibodies, they are bound by a viral protein in the test system – that is, to create a system, you must first obtain this protein and produce it in a laboratory in large quantities. This is being done in Russia as well – for example, scientists from the Institute of Molecular Biology of the Russian Academy of Sciences reported that using one of the viral proteins they successfully detected antibodies to the virus in infected people. As said one of the developers in my facebook, the test system is ready and now there is its clinical trials; if everything goes well, then the test can be registered (now this is done according to an accelerated procedure).

What tests are used in Russia 

The Ozone online store began selling kits for taking biomaterial from the nasopharynx – you can come with it for analysis to one of the Medsi clinics or call a nurse at home. At the same time, Yandex launched a free testing facility. We are talking about PCR analysis for viral RNA, the most accurate and sensitive method. Both Rospotrebnadzor and manufacturers say the probability of detecting the virus is 94–98%. True, most likely, such indicators are achieved under ideal conditions. Practitioners who treat patients with a new coronavirus infection say that in reality the accuracy is 70-80% – this is primarily due to the human factor.

It is already clear that coronavirus pneumonia differs in a specific picture on CT, even if the analysis for the virus gave a negative result – therefore, those who come with symptoms of pneumonia are given tomography. In such cases, the diagnosis is formulated as “probable COVIZ-19”.

Who should do the test on their own

Ideally, for mass testing, the results are collected and analyzed centrally – this helps to better understand how the epidemic is progressing, to determine the number of people with asymptomatic infection, to calculate the proportion of seriously ill or dead. It is unclear whether such a register will be created with the results of analyzes carried out by the same Yandex. It makes sense to test yourself “just in case” if, upon receiving a positive result, you are ready to take action – for a couple of weeks, completely abandon any contacts and exits from the house.

Theoretically, home tests for antibodies may appear – this requires a drop of blood from a finger, but at home it is possible (this is how, for example, glucometers used by people with diabetes work). Some countries are now planning to test a large sample of the population for antibodies in order to understand what proportion of people are already immune to the new coronavirus. So far, it is believed that immunity lasts for several months – after that there will be a repeated risk of infection, but it is assumed that a vaccine will be created before the second wave of infection.

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