Deciphering COVID-19 Testing

By Henrylito D. Tacio

Last March 22, the Philippine Daily Inquirer reported that Singapore has donated 3,000 coronavirus testing kits and a PCR machine (thermal cycler) to the Philippines in its battle against the coronavirus disease 2019 (COVID-19).

Source of information was Foreign Secretary Teodoro Locsin, Jr. who made the announcement on Twitter.

Two other countries – China and South Korea – earlier also donated test kits to the country.

“There is something the public, especially the decision makers, should know about testing for COVID-19,” wrote Dr. Maria Cecilia Lim, a forensic pathologist from the University of the Philippines-Philippine General Hospital, in her Facebook account posted on March 21.

Pathologists, if you care to know, are the doctors in charge of the clinical laboratory in the hospitals and clinics.  They are “the people 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.”

All over the globe, there are several tests available but all these can be classified into two groups based on the technique used: the PCR-based method and the immunologic method (popularly known as “rapid kit”).

Of the two methods, which is better? Dr. Lim handpicked the PCR-based method, as it is the gold standard for diagnosing COVID-19 infections.  “This method detects the presence of the COVID-19 virus in the body so the test becomes positive earlier or even before the symptoms begin,” she explained.

On the other hand, the rapid kit detects the antibodies the body develops after the virus enters the body.  It is detected later, she said, usually around the time the symptoms are present and even after.

Does it mean rapid kits are not reliable?  “We can actually use rapid kits but it depends on what you want to detect,” Dr. Lim wrote.  “The rapid kits detect the presence of antibodies in your body against the COVID-19 and in certain instances may be useful.  However, you do not make antibodies until a few days after you have been exposed to the virus.”

Is there a possibility of using rapid kits for screening the public like the drive-through style which are featured in some Hollywood movies?  “No,” Dr. Lim replied.  “Because the current test kits are usually negative in people without symptoms of the COVID-19 infection.  The tests usually become positive in people with symptoms.”

So, it is better to use the PCR-based testing for screening the public?  Dr. Lim agreed but she said there are numerous limitations including financial.  “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.”

Now, if a test result is negative, does it mean he doesn’t have COVID-19 infection?  “Both PCR and immunologic tests are not perfect,” she pointed out.  “PCR-based tests will be more sensitive in detecting the infection but there are false negatives (patients who have the infection but the test result is negative).

“This may happen in, for example, the early stage of the infection when the number of virus in the body is still too low for the test to detect,” she continued. “False negatives are higher when using the rapid kits.  Believe the saying among doctors – ‘if the test is negative, it does not mean you do not have the disease.’”

How fast is a COVID-19 test? “A rapid kit is so-called because it can give you a result in about 15 minutes, even less,” Dr. Lim said.  “The PCR test usually takes about 6 hours.  An automated PCR machine such as the Roche 6800 which was recently given US FDA (Food and Drug Administration) Emergency Use Authorization is advertised to give up to 96 results in 3 hours.  Unfortunately, we know of no hospital in the Philippines with this machine.”

Aside from RITM, the Department of Health said there are four other subnational laboratories that are capable of testing COVID-19 virus; these are San Lazaro Hospital in Manila, Baguio General Hospital and Medical Center, Vicente Sotto Memorial Medical Center in Cebu City, and Southern Philippines Medical Center in Davao City.

The question is: can any hospital laboratory set up the PCR testing readily?  “That’s a definite NO,” Dr. Lim stressed.  “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 specially setup laboratory in the hospital with at least three separate rooms for processing the specimens to prevent contamination.

“Laboratories which wish to run the COVID-19 PCR tests must also have a special airflow system in place or else the personnel running the test run the risk of getting the virus themselves,” she further said.  “There is a long list of requirements for setting up this laboratory and will take about 2 months to set up.  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 is hoping, though, that someone can 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 (human immunodeficiency virus) and drug tests are being done in the Philippines,” she said.

So, what happens now to the donated rapid kits which the health department has received? “Donated test kits may have escaped FDA approval but no self-respecting clinical laboratory should simply use the test kits on patients,” she warned.  “There are procedures followed by pathologists who head clinical laboratories to validate whether any test, rapid or otherwise, gives accurate results.  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.”

If you want to know how much a PCR-based test cost, at least P6,000, depending on the cost of the brand of reagents.  “Each major reagent of the test costs about P1,500 and there are 3 plus the other materials and minor reagents used for the test,” Dr. Lim said. “UP-NIH (University of the Philippines-National Institute of Health) is currently validating a test which they say will cost P1,500.  We pray it works.” – ###

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