Explainer: What’s the difference between PCR-based and rapid test kits for COVID-19?

Kristine Sabillo, ABS-CBN News

Posted at Apr 01 2020 04:04 PM

MANILA — You’ve probably heard about COVID-19 test kits that can give results in 5 minutes using blood samples.

These so-called instant test kits that look like pregnancy test kits were reportedly being sold in the black market before some brands were eventually approved by the Philippine Food and Drug Administration (FDA).

But if there are already kits like that, why is it taking the Philippine government several days to confirm each COVID-19 case?

This is because these rapid test kits and those used in accredited laboratories are very different from each other. There are also inaccuracy concerns when it comes to test kits that deliver fast results.

Before we get into that, let’s first learn about what health authorities consider the “gold standard” of COVID-19 testing: real-time polymerase chain reaction (RT-PCR) test kits.

PCR TEST KITS

The very first test kits received by the Philippines from the World Health Organization are real-time reverse transcription polymerase chain reaction-based (rRT-PCR).

These kits include reagents and other chemicals used to check if a patient’s sample has the COVID-19 virus.

Such kits can only be used in laboratories with PCR machines. The PCR lab technique allows the detection and amplification of genetic material in body fluids or samples. It has long been widely used in molecular biology.

In January, China released genetic data on the novel coronavirus, allowing scientists to use that information to create their own medical devices and to work on vaccines.

One example of such medical devices is the country’s first locally made kit — the SARS-CoV-2 PCR Detection Kit developed by a team of scientists from the University of the Philippines.

Like other PCR test kits, it requires nose and throat swab samples from a patient.

Dr. Raul Destura, the man behind the UP NIH kit, explained that each kit has three vials. The first is a reagent used to extract the genetic material from the sample. The other is an amber-colored chemical that makes the virus fluorescent for detection. And the third vial is molecular-grade water that serves as negative control to ensure that the results are accurate.

Destura said the actual test will only take two hours but results are released in 24 to 28 hours as samples are often tested by batches.

Healthtek Inc., the company manufacturing the UP NIH test kits, said 25 kits can run tests for 20 to 22 people.

Because it involves handling the live COVID-19 virus, PCR test kits can only be used in laboratories compliant with biosafety requirements. 

As of Tuesday, there are 20 FDA-approved PCR kits in the Philippines.

RAPID TEST KITS

Unlike PCR-based kits, rapid test kits or immunoassay testing uses blood samples.

Such kits are unable to detect the COVID-19 virus. Instead, it measures a patient’s antibodies through the blood sample. 

The Department of Health has repeatedly warned against its use since the kits are prone to “false negatives.”

A health official explained that the kits might be unable to detect antibodies at the early stage of an infection. And because people might end up getting false negatives as a result, they will continue to interact and infect other people in their community.

 

However, just a day after the DOH issued a warning against hospitals using rapid test kits, the FDA announced its approval of 5 brands.

As of Wednesday, there are 6 FDA-approved rapid test kits in the country.

Despite its approval, the FDA reminded the public that the kits should only be used with the supervision of a doctor because it involves mixing a solution.

Each kit is required to have the following label: “This product is strictly for medical professional use only and not intended for personal use. The administration of the test and interpretation of results should be done by a trained health professional. Confirmatory testing is required.”

The FDA also said that the rapid test kits cannot be used for mass testing and will need confirmatory PCR testing. 

It explained that rapid test kits will only be used in some cases such as when there is a need for immediate testing of a patient with severe symptoms or for communities where COVID-19 has long been believed to be circulating.

The FDA also emphasized the need for health professionals to handle the blood samples, which can be a source of other diseases.

While rapid test kits can produce results in just minutes, there are now PCR-based COVID-19 kits that only take 5 minutes of processing. The FDA is hoping to have these kits soon in the country.

In the meantime, Filipinos will have to mostly rely on PCR-based test kits that take 24 to 72 hours to process.