PCR tests, also known as molecular tests, look for pieces of the virus’s genetic material using a lab technique called polymerase chain reaction (PCR). They are the most accurate kind of test for COVID-19 currently available.
PCR samples are usually sent for processing and analysis in a lab, and results can take anywhere from a few hours to several days to arrive. Lab-based PCR tests tend to cost more than other test types. Some point-of-care PCR tests are now available, but they typically require purchase of a dedicated instrument and training to run the tests. If you want to use a point-of-care PCR test to screen members of an organization, you may need to purchase multiple instruments and train several staff members for this purpose. Point-of-care PCR tests typically return results in under an hour.
Antigen tests look for viral proteins. These tests typically provide results within minutes and are very good at accurately identifying people who are carrying a lot of virus. They are not as good as PCR tests are at finding people who aren't carrying as much virus, including children and asymptomatic adults. If your organization is using this type of test, check how well the brand you use works in the population you’ll be testing (adults vs. children, people with symptoms vs. people without symptoms). Many antigen tests still require trained staff run them, but others are now available over the counter for home use. Antigen tests tend to be the least expensive type of test.
Because of their decreased sensitivity, antigen tests have the following limitations:
If you are using antigen tests to screen members of an organization, you may need to test more frequently than you would if you were using a PCR test in order to prevent an outbreak.
If you have symptoms or were recently around someone with COVID, a positive result on an antigen test is usually correct, but a negative test result might not be right. If you just got infected, you may not have enough virus in your system for a rapid test to detect.
Once your virus levels have gone up, a rapid test will show a positive result.
If you have symptoms, it's best to take a second test 48 hours after the first. If you were exposed but don't have symptoms and test negative on both of those tests, it's best to take a third test 48 hours later.You can also get a lab test to confirm your result.
Be sure to follow all of the instructions that came with the test.
Remember, no test is perfect.
FDA — Coronavirus 2019 Test Basics
CDC — Guidance for Antigen Testing for SARS-CoV-2 for Healthcare Providers Testing Individuals in the Community
CDC — Self Testing At Home or Anywhere