![]() ![]() Then you apply this liquid to a test strip that has antibodies specific to SARS-CoV-2 painted on it in a thin line. To run an antigen test, you first treat a sample with a liquid containing salt and soap that breaks apart cells and other particles. These tests use lab-made antibodies to search for antigens from the SARS-CoV-2 virus. Antigen tests, the other major type of coronavirus test, while much faster, are less accurate.Īntigens are substances that cause the body to produce an immune response – they trigger the generation of antibodies. PCR tests are accurate but can take a long time to produce results. Rapid, accurate tests are essential to contain a highly contagious virus like SARS-CoV-2. Lennardywlee via Wikimedia Commons, CC BY-SA Antigen tests Rapid antigen tests – like the two seen here showing negative results – are much faster and easier to perform but are less sensitive than PCR tests. And finally, they aren’t cheap at $100 or more per test. Between sample collection, transportation, amplification, detection and reporting, it can take from 12 hours to five days for a person to get results back. Usually only large, centralized testing facilities – like hospital labs – can conduct many PCR tests at a time. They require a skilled laboratory technician and special equipment to run them, and the amplification process can take an hour or more from start to finish. However, PCR tests have some weaknesses too. ![]() With accuracy that approaches 100%, it is the gold standard for diagnosing SARS–CoV–2. This makes it a highly sensitive and accurate test. The amplifying property of PCR allows the test to successfully detect even the smallest amount of coronavirus genetic material in a sample. The amplified sequence contains fluorescent dye that is read by a machine. Laboratory machines repeat these heating and cooling cycles 30 to 40 times, doubling the DNA until there are a billion copies of the original piece. You’ve now created two copies of coronavirus DNA from the original one piece of RNA. The primers ensure that only coronavirus DNA is amplified. The temperature is lowered, and polymerase, with the help of a small piece of guide DNA called a primer, binds to the single-stranded DNA and copies it. Then, the DNA is mixed with a solution containing an enzyme called a polymerase and heated, causing the DNA to separate into two single-stranded DNA pieces. A health care worker takes the sample and treats it with an enzyme that converts RNA into double-stranded DNA. This is done using a technique called a polymerase chain reaction. This can be a nasal swab or a bit of saliva.įor PCR tests, the next step is amplification of genetic material so that even a small amount of coronavirus genes in the patient’s sample can be detected. The first step for either kind of test is to get a sample from the patient. Karl Mumm via Wikimedia Commons, CC BY-SA Looking for genetic evidence ![]() So what are the differences between these types of tests? PCR tests are extremely accurate but require special lab equipment – like the PCR heating machine seen here – and can take hours or days to perform. Each detects a different part of the virus, and how it works influences the test’s speed and relative accuracy. Two major types of tests are used to diagnose infection with SARS-CoV-2: molecular tests – better known as PCR tests – and antigen tests. I’m a molecular biologist, and since April 2020 I’ve been part of a team working on a National Institutes of Health-funded program called RADx that is helping innovators develop rapid tests to detect when a person is infected with SARS-CoV-2, the virus that causes COVID-19. But do you know which kind of test you got and the strengths and weaknesses of these different tests? Morsa Images/Digital Vision via Getty ImagesĪt this point in the pandemic, you or someone you know has probably received at least one COVID-19 test. All COVID-19 tests start with a sample, but the scientific process goes very differently after that. ![]()
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