Antigen and antibody: 5 things to know about


COVID-19 is a disease caused by a new coronavirus called SARS-CoV-2. WHO first became aware of this new virus on December 31, 2019, when a cluster of cases of “viral pneumonia” were reported in Wuhan, People’s Republic of China.

More effective methods are being developed all the time to determine if we are infected with COVID-19. Generally, PCR tests and antigen tests are distinguished. But do you know what the difference is? In today’s post, we will tell you so that you can clarify all your questions.  There are two types of tests (diagnostic tests) for Covid-19, those that are designed to determine if there is an already confirmed infection, or those that are created to check if there was a previously reported infection. Like almost every product, it has developed varying degrees of effectiveness and reliability, and can be used for different purposes. Rapid tests (also called rapid diagnostic tests (RDTs)) detect the presence of viral proteins (called antigens). A sample of material is obtained from the nasal cavity or from the throat using a swab.

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These tests are less expensive than PCR and provide faster results, although they tend to be less accurate. The results of such tests are most reliable in conditions of intensive circulation of the virus among the population and in those cases when a sample of the material is taken during the period of the greatest infectiousness of the carrier of the infection.  Whereas antigen tests try to detect the presence of proteins on the surface of virus to determine the presence of the pathogen, the PCR test or polymerase chain reaction – tests seek DNA – and other proteins from. Both analysis procedures require a nose swab and can determine if a patient is still contagious. We need fast, accurate, high-performance technology that doesn’t require expensive, sophisticated laboratory equipment or highly trained technicians, but at the moment there is nothing that meets all of these criteria.

Here are five things to know about coronavirus testing:

1.PCR and antigen tests are the form of most common, but they work in different ways.

While antigen tests look for proteins on the surface of a virus to establish the presence of a pathogen, PCR (polymerase chain reaction) tests are designed to look for genetic material called RNA that instructs the virus to make these proteins. This process does not require laboratory work and can take up to 30 minutes, but this speed is achieved at the expense of sensitivity. While these tests are reliable when a person has a high viral load, they are much more prone to false negative results if the person has a small amount of the virus in their body.

Both tests also require taking a swab from the back of your nose or throat as a sample and cannot tell if you are infectious if you test positive, but that is where the similarities end. In the case of PCR, the test sample is sent to the laboratories, where it is heated and cooled using special reagents to convert the RNA of the virus into DNA. This process can take several hours, requires complex laboratory equipment and technicians, and is usually performed one sample at a time. In contrast, antigen tests – often called rapid lateral flow test – work by mixing a sample with a solution that releases certain viral proteins. This combination is then applied to a paper strip that contains a specially designed antibody optimized to bind these proteins, if present.

2.Sensitivity and specificity are the criteria for the usefulness of the test.

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Sensitivity is defined as the proportion of patients with Covid-19 who correctly test positive, and specificity is the proportion of patients without infection that the test correctly identifies as negative.

3.Antibody test result can be useful to measure the persistence of responses to vaccines

Antibodies are soldiers (like free online support service) that are used by the immune system in response to a foreign invader – in this case SARS-CoV-2. It was originally hoped that antibody test results would enable us to diagnose the disease quickly and easily. But it turns out that the tests do not give positive results for two to four weeks. if your antibody test comes back positive, this information will tell you little other than the high likelihood that you have contracted Covid-19 in the past. It is also unclear how long Covid-19 antibodies last in the body, and that anyone who tests positive for the antibodies will no longer be infected with the virus. These tests can be useful for assessing the spread of Covid-19 at the population level – for example, what percentage of the population and which ethnic groups are infected with Covid-19, and for measuring the persistence of vaccine responses.

4.Until rapid tests become more accurate, negative results should not be used to reward risky activities.

Governments are keen to use rapid tests because they are cheaper and faster to deploy for mass vaccination campaigns, but because they have limitations in terms of accuracy, it is important not to use negative results for riskier activities, such as meeting the elderly or vulnerable people. While rapid tests are good for identifying people with high viral loads, it is not yet clear what the viral threshold should be to prevent contagion. With Covid-19, those infected experience a peak viral load early in the infection, but viral RNA can persist for week or even months.

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5.When it comes to rapid tests, the person conducting the test can be critical.

The researchers found confirm that in a population of mostly symptomatic people, the sensitivity of the test dropped to about 58% when administered by self-trained personnel, compared with 73% when tested by trained research nurses and 79% when tested. tested by lab scientists. In a study that looked at people without symptoms, the sensitivity dropped to about 49% when compared to PCR tests. Thus, it can be said that the more experienced people conduct the test, the fewer cases will be missed.  In the UK, an antigen test called the Innova Sidestream Test has been tested in the city of Liverpool as part of government plans for mass vaccinations in the country. the goal was to allow workers to return to offices and allow families to embrace their loved ones again in nursing homes.

PCR tests are processed in the laboratory, so the probability of error is much lower. Test makers are also trying to develop home tests, but given the lessons we’ve already learned about how the accuracy of rapid tests depends on who runs them, this is a problem. Some countries, such as the United States, advise getting a PCR test if people with symptoms test negative for a rapid antigen test to confirm the result.

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