An antigen test, often referred to as a rapid or fast COVID-19 test, is a viral test, one of the two types of tests used to detect COVID-19. Rapid antigen tests are considered to be one of the simplest and quickest ways to test yourself for COVID-19 and have been recommended by many authorities and governments as a cost-effective way to mass test populations.
This article covers the basics of rapid antigen tests, the accuracy of the tests, how they work, and where to find reliable and trustworthy rapid antigen tests.
What is an antigen?
According to Harvard’s Medical Dictionary of Health Terms, an antigen is any substance that the body recognizes as harmful or foreign, which induces the immune system to produce antibodies against it1.
How do antigen tests identify COVID-19?
Rapid antigen tests identify protein fragments on the surface of the coronavirus to identify the presence of the pathogen amongst people doing the test2. Samples are taken from subjects by swabbing inside the nose or mouth.
How are antigen tests administered?
Rapid antigen tests are commonly administered by using a sterile cotton swab and taking samples from the nasal cavity or mouth and adding a liquid solution to get a result.
Here is a short breakdown of the procedure:
- Collect the sample by swabbing and rotating the cotton swab inside both nostril
- Place the swab inside the testing well
- Add the liquid testing solution
- Wait for 15 minutes to get a result
How accurate or reliable are antigen tests?
The accuracy and reliability of rapid antigen tests is often debated. Compared to polymerase chain reaction (PCR) tests, rapid antigen tests are slightly less accurate.
Generally, test accuracy is measured using sensitivity and specificity.
- Sensitivity is defined as the ability to correctly identify subjects with COVID-19.
- Specificity is defined as the ability to correctly identify subjects without COVID-19.
PCR tests have been shown to be up to 100% accurate, although accuracy varies depending on which test is used. Some tests have been found to present false-negative result rates of 15% to 20%3.
In comparison, rapid antigen tests have been found to show false-negative rates of up to 20%4. 20test’s rapid antigen test kit accurately identifies 92% of people who do have COVID-19, and correctly identifies 99.67% of people without COVID-19.
Just to clarify, a false negative is when a subject is incorrectly diagnosed as not diseased. For example, let’s say that someone has COVID-19 and takes a test, if the test result returns a negative result, despite actually currently being infected, this would be considered a false negative result. The test did not correctly identify someone with the coronavirus.
What are antigen tests used for?
Rapid antigen tests are used to identify people that currently have the virus5. Past infections can be identified using other types of tests.
Other than for identifying COVID-19, antigen tests are commonly used to identify:
- Streptococcus infections
- the influenza virus
Where can I get a rapid antigen test?
Depending on where you live, rapid antigen test kits can be found in physical stores and buildings like pharmacies, local healthcare services, and facilities.
They can equally be purchased online from a variety of websites. Make sure that you buy your test kit from a reliable and trustworthy website to ensure the accuracy of your test.