RT-PCR vs Rapid Test Kits. What’s in a name?
RT-PCR
These test kits use swabs from your nose and throat which are designed to capture the genetic material of the virus. SARS-CoV-2 is an RNA virus, so its genetic material is more transient and fragile than DNA. (READ: COVID-19 Diagnostics Explained Read more from Asian Scientist Magazine)
Because of that, samples should ideally be transported to testing laboratories on ice or in special media to prevent them from degrading. Once at the lab, the RNA must first be converted to DNA using an enzyme called reverse transcriptase. Then, specific sequences of DNA (primers) designed to recognize complementary virus sequences are added, so that another enzyme can make a copy of a short length of viral DNA. This process is repeated for 20-30 cycles, exponentially amplifying the amount of viral DNA so that it can be detected.
RT-PCR remains the gold standard for testing, and it takes 24-72 hours, besides that they also need to be transported and done in the appropriate labs and by highly skilled professionals. (READ: Here’s How Coronavirus Tests Work—and Who Offers Them)
Rapid Test Kits
Rapid test kits measure a patients antibodies using blood samples. They do not confirm if one has CoviD-19 and are therefore prone to false negatives. Instead of detecting viral genetic material, rapid tests kits target the immune response of the person being infected, looking out specifically for antibodies against the virus or virus antigens.
The trouble is that antibodies only develop several weeks after an infection, which means that antibody-based tests might miss asymptomatic cases or people in the earliest stage of the disease. Antibodies are sometimes not detected in the early stages of the infection, that is why a false negative test would create a false sense of security, and they may end up continuing to infect their communities if they use it as basis for their status and start walking around. The test is also prone to false positives as it may react to other coronavirus infections even if it’s not caused by SARS-CoV-2. (READ: Explainer: What’s the difference between PCR-based and rapid test kits for COVID-19?)
That is not to say that antibody-based tests are not useful. On the contrary, antibody-based tests have proven to be crucial in linking clusters of infection, by detecting people who were infected but discovered too late to test positive via RT-PCR. As RT-PCR looks for virus RNA, it will only give a positive test result if there is an ongoing infection. On the other hand, antibodies can persist for months or years, allowing tests to identify anyone who has ever been infected.
Rapid test kits are used, as compliance to the FDA. They 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.
Like any medical test, a professional should be the one to handle these tests and authorities are continually cracking down on people selling fake test kits – additionally they are not and should not be sold in pharmacies (or any store for that matter)
There is hope though, as there are developments for PCR test kits that could provide results in 15 minutes. Problems that we might encounter along the way are the unavailability of Testing centers and lack of professionals capable of handling these tests. (READ: EXPLAINER: What to expect from the Philippines’ expanded coronavirus testing)
Who are being tested?
Guidelines suggest that people at risk should be tested. These are suspected cases, people with travel history with or without symptoms, and health care workers with or without symptoms. Suspected cases are divided into subgroups from highest to lowest priority.
Sub-group A:
Patients or health workers showing severe or critical symptoms, and who had exposure to a confirmed case or a history of travel
Sub-group B:
High-risk or vulnerable patients and health workers showing mild symptoms, and who had exposure to a confirmed case or a history of travel
Sub-group C:
Patients or health workers with mild symptoms, and who had exposure to a confirmed case or a history of travel
Subgroup D:
Patients or health workers who are asymptomatic but have a history of travel or had exposure to a confirmed case.
These categories are made because of shortages of test kits, with priority given to sub group A and so on. Regular people may also be tested, especially if they are in close contact to suspected cases. (READ: FAST FACTS: Steps in a coronavirus PCR-based test)
With or without tests suspected persons are required to observe a 14 day isolation period – they are to be raised from their quarantine once they are tested negative. But due to test kit shortage concerns again, without tests they can be raised from quarantine after 14 days when they no longer show any symptoms – which if we remember how CoviD-19 works, is very very risky. (READ: COVID-19 Testing: RT-PCR Test vs. Rapid Antibody-based Test)
For more on our local testing here’s a DOH infographic from their facebook page.
