Understanding COVID-19 Testing

In navigating the new normal, chances are, you or your loved ones have been, or will be required to take a COVID-19 test.

The reasons will vary.  It could be for travel, to be allowed to work, or simply to find out if one is currently contagious or has been infected in the past.

As of this writing, COVID-19 has claimed the lives of 1.4 million people around the world.

There are currently three types of tests you might be hearing that are related to the SARS-CoV-2 virus and COVID-19.

Here’s a brief description of each:

RT-PCR (Reverse Transcriptase PCR) test

The COVID-19 RT-PCR test is currently considered the gold standard in COVID-19 testing.  It detects the virus’ genetic material. Most, if not all countries, base their official number of cases on those done via PCR tests, not by any other method.

This is also the test required by most authorities in allowing inbound travelers. 

Usually, testing is done through a nose and throat swab test.  A six-inch stick (like a long cotton bud), is inserted in each nostril, and some include the throat, to get secretion samples.

This sample is processed in a laboratory to detect the genetic material of the SARS-CoV-2 virus.  A positive result means the virus’ RNA is present in the patient.  It could mean he is currently infected or was previously infected.  Remember the virus’ RNA can stay in a patient even if he is no longer infectious.

A negative result is generally considered a safety pass, although no testing is 100% accurate.  

The margin of error on an RT PCR test can be due to handling of samples, and delay in processing. Samples need to be kept in temperatures of -8 to -20 degrees celsius, and the ideal time for samples to be processed is not later than 72 hours after collection. 

In the Philippines, tests usually come out in 24 to 72 hours or longer, depending on the load of the laboratory. 

Antigen test

The COVID-19 Antigen test detects certain proteins of the SARS-CoV-2 virus.  This means if the proteins are present, then so is the virus.

The method of testing is also through a nose and/or throat swab, similar to RT-PCR.

The antigen test is particularly useful if a person is currently infected or at the height of infection.  That’s because antigens would be at their peak, and have more chances of being detected.

Unfortunately, it is not very accurate at the first few days of exposure.  This is because it usually takes a few days before the antigens are detected in one’s system.  So one could be exposed at an early stage — and might already be infectious — and get a negative result.

Despite chances of false negative results, an antigen test could still be useful, because of its lower cost and fast result.  Antigen test results can come out as quickly as 15 minutes after the swab. 

If one suspects possible exposure, an antigen test could be taken a few days after the suspected exposure (best to stay isolated in the interim).  If it yields positive, there’s almost a sure infection.  A confirmatory RT-PCR can follow or medical treatment as advised by a professional.

Antibody test

According to the Mayo Clinic, “COVID-19 antibody testing, also known as serology testing, is a blood test that’s done to find out if you’ve had a past infection with SARS-CoV-2, the virus that causes coronavirus disease 2019 (COVID-19). An antibody test can’t determine whether you’re currently infected with the COVID-19 virus.”

“Antibody testing for COVID-19 may be done if:

  • You had symptoms of COVID-19 in the past but weren’t tested
  • You’re about to have a medical procedure done in a hospital or clinic, especially if you’ve had a positive COVID-19 diagnostic test in the past
  • You’ve had a COVID-19 infection in the past and want to donate plasma, a part of your blood that contains antibodies that can help treat others who have severe cases of COVID-19”

Webmd further says, “The antibody test isn’t checking for the virus itself. Instead, it looks to see whether your immune system — your body’s defense against illness — has responded to the infection.”

A Filipino doctor and testing expert, Dr. Mike Vergara however says there are antibody test kits that could determine current infection.  “Some antibody kits detect IgM and not just IgG”.  IgM and IgG are types of immunoglobulins that attack viruses such as SARS-CoV2.  IgM is the first set of immunoglobulins produced by the body to determine if a perceived intruder is foreign or not.  If it is identified as foreign and threatening, the IgM calls for “backup” and the IgG takes over.  The IgG is also the one giving the body immunity.  

So a positive IgM (present in some antibody kits) means current infection, and a negative IgM, but positive IgG means past infection.

Purpose and Timing of tests

All three types of tests — PCR, ANTIGEN and ANTIBODY have their place in COVID-19 detection and prevention of spread:   

  • Before one becomes infectious – RT PCR can detect
  • Currently Infectious – RT PCR, ANTIGEN and ANTIBODY (with IgM measure) can detect.  Although ANTIGEN and ANTIBODY may miss the early parts of exposure 
  • Past Infection – RT PCR will still be positive, ANTIGEN will yield negative, ANTIBODY IgG will detect past infection and current immunity.

Reliability of tests

The reliability, efficacy and sensitivity of the type of tests depend on the institutions conducting it and the brands being used.  Always go for reliable and reputable agencies and products.

Developing Technology 

New tests and procedures on determining SARS CoV2 infections are continuously being developed, and so are vaccines.  As of this writing, at least three firms have reached final stages of vaccines testing. 

A detection method using just saliva is also underway. 

The best way to avoid spreading COVID-19

The best way to avoid spreading COVID-19 is still to go on a 14-day quarantine before travel or engagement.  If no symptoms come out, it is highly likely that one is negative from the virus, even without testing.  It is the best practice to employ before seeing loved ones. And of course the frequent washing of hands and wearing of face masks.

Definition of Terms

COVID-19 – The name of the disease caused by the novel coronavirus, SARS-CoV-2, and is short for “Coronavirus Disease 2019.” (Source: WHO)

SARS-CoV-2 – The name of the novel coronavirus that causes COVID-19 disease. (Source: WHO)

Coronavirus – A family of viruses that cause illness ranging from the common cold to more severe diseases, such as Middle East Respiratory Syndrome (MERS-CoV) and Severe Acute Respiratory Syndrome (SARS-CoV). The novel coronavirus recently discovered has been named SARS-CoV-2 and it causes COVID-19. (Source: WHO)

Coronavirus – A family of viruses that cause illness ranging from the common cold to more severe diseases, such as Middle East Respiratory Syndrome (MERS-CoV) and Severe Acute Respiratory Syndrome (SARS-CoV). The novel coronavirus recently discovered has been named SARS-CoV-2 and it causes COVID-19. (Source: WHO)

*This article, though thoroughly researched, is not a substitute for a medical consultation. It is still best to speak with a medical expert on testing questions.

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