What tests are used to diagnose COVID-19?
The FDA approved these types of tests for diagnosing a COVID-19 infection:
RT-PCR test. Also called a molecular test, this COVID-19 test detects genetic material of the virus using a lab technique called reverse transcription polymerase chain reaction (PCR). A fluid sample is collected with a nasal swab or a throat swab, or you may spit into a tube to produce a saliva sample.
Results may be available in a few hours or or longer in locations with test processing delays — if sent to an outside lab. RT-PCR tests are very accurate when properly performed by a health care professional.
Antigen test. This COVID-19 test detects certain proteins in the virus. Using a nasal swab to get a fluid sample, antigen tests can produce results in 15 minutes. A positive antigen test result is considered accurate when instructions are carefully followed. But there's an increased chance of false-negative results — meaning it's possible to be infected with the virus but have a negative result. Depending on the situation, the health care provider may recommend a RT-PCR test to confirm a negative antigen test result.
When is Antibody test done and why?
Antibody testing, also known as serology testing, is usually done after full recovery from COVID-19. Eligibility may vary, depending on the availability of tests. A health care professional takes a blood sample, usually by a finger prick or by drawing blood from a vein in the arm. Then the sample is tested to determine whether you've developed antibodies against the virus that causes COVID-19. The immune system produces these antibodies — proteins that are critical for fighting and clearing out the virus.
If test results show that you have antibodies, it can mean that you have been infected with the COVID-19 virus in the past or you have antibodies after being vaccinated. It may also mean that you have some immunity. However, having antibodies may not mean you're protected against reinfection with COVID-19. But they can help prevent severe disease. The level of immunity and how long immunity lasts aren't yet known and continue to be studied.
The timing and type of antibody test affects accuracy. If you have testing too early in the course of infection, when the immune response is still building up in your body, the test may not detect antibodies. So antibody testing is not recommended until at least 2 to 3 weeks after your symptoms started.
Another benefit of accurate antibody testing is that people who've recovered from COVID-19 may be eligible to donate plasma, a part of their blood. This plasma could be used to treat others with severe disease and boost the ability to fight the virus. Doctors call this convalescent plasma.
COVID-19 Vaccination Is a Safer, More Reliable Way to Build Protection
Getting a COVID-19 vaccine is a safer, more reliable way to build protection than getting sick with COVID-19. COVID-19 vaccination helps protect you by creating an antibody response without you having to experience sickness, potentially including severe illness.
Getting sick with COVID-19 can have serious consequences.
Getting sick with COVID-19 can cause severe illness or death, even in children, and we can’t reliably predict who will have mild or severe illness.
You may have long-term health issues after having COVID-19. Even people who do not have symptoms when they are first infected can have these ongoing health problems.
While people can get some protection from having COVID-19, the level and length of that protection varies.
Immunity (protection) from infection can vary depending on how mild or severe someone’s illness was and their age.
Immunity from infection decreases over time.
Importantly, there is still not an antibody test available that can reliably determine if a person is protected from further infection.
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