Rapid test kits not used in swabbing exercises in Singapore as they are not sensitive enough

Test kits that can determine if a person has Covid-19 in minutes are not being used in national swabbing exercises in Singapore as they are not sensitive enough to detect every infection.

Associate Professor Raymond Lin, director of the National Public Health Laboratory at the National Centre for Infectious Diseases (NCID), told The Straits Times earlier this month that this was because rapid tests can give false negative results, missing true cases.

Prof Lin said then: "Currently available antigen rapid test kits can miss as many as one in six cases, or even more. If we miss cases, we will have more outbreaks."

The NCID will continue to look for test kits that are fast and accurate, he added.

More than 120 Covid-19 diagnostic test kits have received provisional authorisation from the Health Sciences Authority, ranging from polymerase chain reaction (PCR) kits to antigen and serology ones.

All three work differently.

PCR tests look for fragments of the virus' genetic material in a patient sample and are considered the "gold standard" test for Covid-19.

But the entire process - from swabbing a patient to sending the sample to a laboratory and the PCR process itself - can take up to a day.

It can also be costly, and requires trained personnel and specialised equipment to administer.

Antigen test kits, on the other hand, are point-of-care tests that look for proteins on the virus surface and can yield quick results, usually within minutes.

Serology tests, which detect the presence of antibodies, are mainly used to tell if a person has been infected in the past, and not to diagnose patients.

However, experts have noted that because rapid diagnostic tests are cheaper and less invasive than PCR tests, their prudent and repeated deployment could supplement national measures to control Covid-19.