What is the difference between rapid and PCR tests?

COVID-19 has been a prominent part of our lives for around two years. Over that time, our testing options have grown to include several types of tests that can be done at home. 

To control disease in a pandemic you need rapid and accurate testing. The PCR COVID test provides an accurate result but it is slow. Rapid COVID testing shows results in 15 to 20 minutes but it is not as accurate as the PCR COVID test. In this article, we examine the differences between the PCR and rapid tests and discuss which is the appropriate choice.

How do COVID tests work?

Both rapid COVID testing and PCR COVID tests require a nasal or throat swab. The tests themselves are, however, vastly different. 

Rapid antigen test

To do the rapid antigen test, the sample is mixed with a solution containing salt and soap. This releases a set of viral proteins. The solution is then placed on a strip of paper. The paper contains an antibody that will react in the presence of COVID proteins. 

Rapid COVID testing can return a result within 15 minutes and requires no laboratory intervention. These tests are, however, not as reliable as the PCR COVID test. The rapid test may return a negative result when the viral load of the tested person is low. Under certain circumstances, it can also produce a false positive.

PCR test

The PCR COVID test is the gold standard for testing. It is slow, however, and can take several hours to return a result. The test uses a polymerase chain reaction (PCR) to convert the virus’ RNA into DNA for identification. Laboratory technicians do the test using sophisticated scientific equipment in a laboratory. 

The PCR results are very accurate, so this is the test you need to show proof that you are COVID-19 negative. 

Antigen vs pcr test

A nasal or throat swab is required for both the rapid antigen and the PCR test. The PCR COVID test is the more accurate of the two tests. It does, however, take longer to get results because trained technicians must do the test in a laboratory. It takes between 24 and 72 hours to get the PCR results. 

Rapid COVID testing is not as sensitive as the PCR test and can give a false result. The advantage of the rapid test is that you will have the results within 15 minutes. You need no special training to run the test or interpret the outcome. 

Which type of COVID test should I take?

The right test for you will depend on the reason for taking the test and the circumstances that led you to consider it. 

When to take a rapid antigen test

Rapid antigen tests have been successfully used to prevent cross contamination in communal living environments and workplaces. It is also used by people who have tested positive for COVID-19 and want to know whether they are still infectious. 

When to take a pcr test

You should take a PCR test under the following circumstances;

• Within three days of showing symptoms of COVID-19

• If you know or suspect that you may have been exposed to COVID-19 

• A PCR test is a requirement for international travelers who must show a negative result within 72 hours of departure.

What does a false positive or false negative mean?

The PCR COVID test is both specific and sensitive. This means that if you don’t have COVID-19, there is a high probability that it will return a negative test. If you have COVID-19, it is also highly likely that the PCR test will pick it up. Still, the test can return false results.

If the viral load is low, the test may present a false negative. This is most likely at the early and late stages of infection. Laboratory errors, like cross-contamination, is the most likely cause of false positive results.

The rapid antigen test is most likely to return a false positive test as it sometimes picks up antibodies from other corona viruses. There is also a high risk that the test could produce a false negative because the test relies on a higher density of virus in the sample that a PCR does. 

A study done in August 2021 showed that rapid COVID testing performed at home returned a correct negative 97.1% of the time. It correctly identified positive results in 78.9% of cases. 

What if I have symptoms but get a negative rapid test result?

If you have COVID-19 symptoms and you receive a negative result from the rapid antigen test, it may have received a false negative. Take a PCR test to confirm the result. This is especially important if you have been exposed to the virus. 

Rapid vs PCR which should you take?

Both rapid antigen and PCR tests play an important role in controlling the spread of COVID-19. Rapid COVID testing is quick and easy. It is useful for testing and controlling COVID-19 in communal environments and in the workplace. It is, however, not as accurate as the PCR test and the results are not accepted for travel purposes. In the case of a doubtful rapid antigen result you may have to confirm the outcome with a PCR COVID test.

FAQs

How fast is a PCR test?

A PCR COVID test takes about 1.5 to 2 hours to do in the laboratory. Depending on the backlogs, you could wait a day or more for the result.

How fast are rapid COVID tests?

You can get a result from a rapid COVID test in 15 to 20 minutes at home, in a doctor’s office, or at a drive-by testing facility.

Should I get a rapid or PCR test?

It depends on the reason for the test. If you’re traveling abroad you may have to have a PCR. If you need a quick answer, the rapid test is better. If the rapid test returns a negative result and you’ve been exposed to COVID-19, you may have to go for a PCR test anyway.