RT-PCR vs. Rapid Antigen Test: When Should You Take Either One and Which Gives the Most Accurate Results?

As COVID-19 cases continue to rise due to the Omicron variant, testing has also become more critical. Many people with or without symptoms would use either RT-PCR or rapid antigen tests to determine whether they are infected with SARS-CoV-2.

So, when should people use the RT-PCR test, and when is using rapid antigen test suitable? Is one of them more prone to false-negative results? Regardless of the situation, here are the differences between RT-PCR and rapid antigen tests.

When RT-PCR Test Should Be Done?

The reverse transcription-polymerase chain reaction (RT-PCR) test is the golden standard for detecting SARS-CoV-2. That is why it is the most preferred COVID-19 test.

According to the Centers for Disease Control and Prevention (CDC), the RT-PCR test can detect small amounts of the genetic material of SARS-CoV-2 in a sample because it has to amplify properties that make them highly sensitive for diagnosing COVID-19. But its high sensitivity could also mean that RT-PCR tests can give positive results even if the person is no longer contagious.

That means the RT-PCR tests could say that a person still has COVID-19 even after three or four weeks after recovering because it picks up the infection and small fragments of the virus, CNN reported. Furthermore, Dr. Albert Ko from Yale School of Public Health said that the prime time to take the RT-PCR test is when exposed to a COVID-19-infected person or are experiencing symptoms.

Knowing early that an infection is possible can help prevent transmission. Epidemiologist Emily Somers from the University of Michigan said that infected individuals are most contagious two days before symptoms or a day or two after symptoms started to appear.

Ko explained that it takes time for the virus to replicate enough to be detected. However, RT-PCR test can easily detect the virus after exposure compared to the rapid antigen test.

When Rapid Antigen Test Should Be Done?

A rapid antigen test, also known as a rapid lateral flow test, is taken days after getting infected to confirm whether a person is still infectious or not. The current isolation guidance of CDC states that if a person has access to a coronavirus test and wants to take it, the best type of test is a rapid antigen test and use it toward the end of their five-day isolation period.

According to Healthline, a rapid antigen test is a smart tool to have in the medicine cabinet because it helps detect the virus in asymptomatic cases or those with minor symptoms who may have been exposed to an infected individual. Infectious disease expert Dr. Ting Ting Wong said that asymptomatic people should have two antigen test results taken five days apart to be called free of the virus.

However, if the person starts to show symptoms and the results from the rapid antigen test come back negative, the best course action is to use an RT-PCR test to confirm the result. Wong noted that rapid antigen tests miss about one-third of actual infections, which means it is not sensitive enough to detect SARS-CoV-2 in the body.

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