Primer on coronavirus testing

By Filane Mikee Cervantes

March 26, 2020, 6:12 pm

MANILA – It cannot be overemphasized enough that widespread coronavirus testing is crucial to contain the spread of the pandemic.

In fact, World Health Director-General Tedros Adhanom Ghebreyesus has urged all countries to “test, test, test” for coronavirus.

The Philippines, however, still struggles to ramp up testing due to a limited number of test kits.

Under the Department of Health’s (DOH) decision tool, those who have been showing severe symptoms of the disease, as well as vulnerable sectors, such as the elderly and high-risk pregnant women, will be prioritized for testing.

Several countries have donated testing kits to help the Philippines combat the coronavirus disease.

The Food and Drug Administration (FDA) has so far approved nine Covid-19 test kits for commercial use.

Despite these developments, the slow rollout of tried-and-true polymerase chain reaction (PCR) test kits for coronavirus can be attributed to the stringent procedures to ensure their reliability.

Stringent requirements in setting up PCR testing labs

Clinical pathologist Maria Cecilia Lim said there is a “long list of requirements” for setting up a hospital laboratory for PCR testing, noting that such a facility would take about two months to establish.

“The current supply of PCR test kits approved by our FDA can be used by a variety of machines but not one machine. A molecular pathology laboratory is a special setup laboratory in the hospital with at least three separate rooms for processing the specimens to prevent contamination,” Lim said.

“Laboratories that wish to run the Covid-19 PCR tests must also have a special airflow system in place or else the personnel running the tests run the risk of getting the virus themselves,” she added.

Lim said testing requires trained staff and the right equipment for it to be successful.

“The personnel also will have to be trained for a few weeks. If someone is selling you a single machine to run the PCR tests for Covid-19, think twice,” she said.

Difference between PCR method, rapid test kits

She described the PCR method as the “gold standard” for diagnosing Covid-19 infections, but other faster alternatives have been developed such as the rapid test kits (RTKs).

A rapid kit is so-called because it can give a result in about 15 minutes, while the PCR test usually takes about six hours.

She highlighted that the RTKs cannot help in the early detection of Covid-19, as compared to the PCR method, which detects the presence of the virus in the body even before the symptoms begin.

“The rapid test kit, on the other hand, detects the antibodies the body develops after the virus enters the body. It is detected later, usually around the time the symptoms are present and even after,” Lim said.

This means that the rapid kits test negative in people without symptoms of the Covid-19 infection.

“The tests usually become positive in people with symptoms,” she said.

She said the PCR method-based tests are better, but numerous limitations, including financial, restrict its accessibility for mass testing.

“The most important limitation is that these methods need expensive equipment and a very special setup which is only available in selected hospitals like RITM (Research Institute for Tropical Medicine) and St. Luke’s Medical Center,” she added.

Lim argued that both tests are far from perfect, raising the possibility of getting a false negative result, which indicates that a person does not have a disease when the person actually does have it.

“PCR-based tests will be more sensitive in detecting the infection but there are false negatives. This may happen in, for example, the early stage of the infection when the number of viruses in the body is still too low for the test to detect,” she said.

“False negatives are higher when using rapid kits. Believe the saying among doctors - ‘if the test is negative, it does not mean you do not have the disease’,” she added.
Lim said she expects better and faster PCR test kits to roll out in the near future.

“There will be test kits that will be run on a single machine in platforms more available throughout the nation and require less stringent room requirements. Better, more accurate rapid test kits will also roll out hopefully within six months,” she said.

“The target is to discover a rapid kit that can be used for screening everyone with positive test results being sent for a confirmatory test using PCR-based technique. This is how testing of HIV and drug tests are being done in the Philippines,” she added.

Validating test kits
Lim said while several test kits have been donated, these still have to be validated and tested before distribution.

“Donated test kits may have escaped FDA approval but no self-respecting clinical laboratory should simply just use the test kits on patients. There are procedures followed by pathologists who head clinical laboratories to validate whether any test, rapid or otherwise, gives accurate results,” she said.

“It means that each brand and each batch of tests are compared with a gold standard test which itself should have been validated by the laboratory using it,” she added.

Lim noted that several hospital laboratories are starting to validate their own PCR-based tests with FDA approval.

The DOH has also designated some hospital laboratories to do the PCR-based tests to increase the testing capacity and decrease the workload on RITM.

“If a local government or a hospital owner wishes to set up the PCR testing in their hospital laboratory, talk to the hospital pathologist first and discuss the pros and cons of setting up the laboratory before buying anything,” she said.

“The pathologists are the doctors in charge of the clinical laboratory in hospitals and clinics. They are the ones who ensure that the test result a patient gets is as accurate as possible, not only by making sure that there are quality protocols in place in the laboratory, but also by validating each new test kit and equipment in the laboratory before they are used on patient samples,” she added. (PNA)