Your Covid-19 questions answered

What is the difference between a rapid antigen and PCR test?

The National Institute for Communicable Diseases says PCR tests detect the Omicron variant. File Photo
The National Institute for Communicable Diseases says PCR tests detect the Omicron variant. File Photo
Image: REUTERS/Loren Elliott

As the number of Covid-19 cases increases, so does the need to test more people. 

The reason for this is that accurate and reliable testing has proven to be an effective way to slow the spread of the coronavirus to save lives and reduce the burden on healthcare systems. 

There are two types of Covid-19 tests — polymerase chain reaction (PCR) test and rapid antigen — recommended by government to test for the virus. 

What is the differenc?

According to government, PCR tests are regarded as the “gold standard” for Covid-19 testing. 

A sample is taken from the nose or throat and sent to a lab where it undergoes a process to check if the virus is present. 

PCR tests are recommended for diagnosing active Covid-19 infection. Results are normally available within a day.

“A PCR test is a molecular method that detects genetic material from the virus and is very accurate, but results take about 24 hours,” said government. 

Antigen tests are cheaper, give a result in about 15 minutes but are less accurate.

A rapid antigen test works by looking for proteins on the surface of the virus. As with PCR tests, samples are usually taken from the nose or throat but can be tested on site.

The World Health Organisation said antigen tests typically have high specificity, which means the chance of false positives is low, but they are significantly less sensitive than PCR tests.

Which test is likely to pick up Omicron?

According to the National Institute of Communicable Diseases indications are PCR tests can detect the Omicron variant of the virus. 

The tests, the costs of which have been reduced from R850 to R500, are used to determine if there is specific genetic material from the coronavirus present.

“A PCR test is a nucleic acid-based test, RNA in the case of Covid-19. The test uses a set of enzymes technologies to accurately detect Covid-19 specific genetic markers,” the Council for Scientific and Industrial Research told TimesLIVE.

The institute said the tests check for multiple targets in case there is a variant present.

“The PCR tests typically detect at least two different SARS-CoV-2 targets, which serve as a backup in the case of a mutation arising in one.

“Analysis of the mutations in the nucleocapsid (N gene) of B.1.1.529 viruses suggests rapid antigen tests should be unaffected. However, verification of this is under way,” it said.

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