RT-PCR and other Covid-19 tests
>> Saturday, August 28, 2021
WELLFULL
Victor
Romulo Gallardo Dumaguing, MD
Understandably, doctors are challenged to distinguish one from the other while the turn of events has spawned fear and paranoia among the all citizens of the world considering the fact that there have been many breakthrough Covid 19 cases even in those who have had their complete set of vaccines.
An ideal laboratory test must have sensitivity and specificity. A test is sensitive if it has the ability to identify correctly persons who have the disease whereas a test is specific if it has the ability to identify persons who do not have the disease.
The RT-PCR test has both a high percentage of sensitivity and specificity that’s why it is still the gold standard among the diagnostic tests for Covid 19 infection. In reality, the complete name is rRT-PCR test, r is real time, Reverse transcriptase, Polymerase chain reaction. It is a NAAT- nucleic acid amplification test which detect the existence of the genetic material of the SARS-CoV 2. Its accuracy and reliability is ensured by very stringent requirements; done in highly controlled sophisticated settings, performed under aseptic conditions to avoid contamination and performed by skilled and trained personnel.
In its simplest sense, the procedure involves the so-called “thermal cycles” to make millions –hence the word amplification or multiplication, if you may-of the genetic material of the Covid 19 virus, to reach a crucial amount to produce fluorescent light in the instrument, which would indicate a positive result.
As many of patients have experienced, the ideal specimen is a nasopharyngeal swab because the spread of the virus is through droplet transmission shown in sneezing, coughing, loud talking, therefore the nose harbors the microbe. Of course, the virus may also be picked up from inanimate objects like tables, chairs on which the virus landed and is transferred unwittingly by persons who habitually touch their face, nose and eyes. A throat swab is also done because the nasopharynx continues its descent into the oropharynx- throat area- and into the laryngopharynx and unto the bronchial tree of the lungs.
The Rt-PCR test is dependable and reliable test because it can detect even low virus load, thus it would be useful in catching super spreaders who at the moment may be asymptomatic but have had a close physical encounter with a Covid 19 active patient.
ANTIGEN test is used to detect one of the 79 proteins or the surface receptors of the SARS-CoV 2 microbe which is situated on its shell or envelop. It is also called Rapid Covid 19 test and it has the advantage of being done in less stringent environment like triage areas or in border control points, with the results obtained in 30-45 minutes, in contrast to the rather long 2-3 days turnaround results of RT-PCR test.
Depending on the health status of the person who tested positive with the antigen test- meaning are there now premonitory concerning signs and symptoms of an impending full-blown Covid 19 disease or still asymptomatic- thus advice would range from immediate RT-PCR test, hospitalization , isolation and other quarantine protocols.
ANTIBODY testing, as the name implies is simply to detect the presence of antibodies mounted by the immune system of the person/patient against the antigen- found in the surface receptor of the virus. It does not have as much clinical significance and importance as those of the RT-PCR test and Antigen test in the diagnosis and prognosis (possible outcome) of Covid 19. A positive result simply means presence of antibodies probably to a previous exposure to the virus.
With the emergence of variants of viruses, not only the corona species, it’s expected there would be more diagnostic tests with high sensitivity and specificity. Meanwhile, the RT-PCR test is thankfully accurate and reliable as the alpha, beta, delta variant dance the lambada with the Peruvian lambda.
Next Week: Glossary of Terms in Infectious Diseases
Understandably, doctors are challenged to distinguish one from the other while the turn of events has spawned fear and paranoia among the all citizens of the world considering the fact that there have been many breakthrough Covid 19 cases even in those who have had their complete set of vaccines.
An ideal laboratory test must have sensitivity and specificity. A test is sensitive if it has the ability to identify correctly persons who have the disease whereas a test is specific if it has the ability to identify persons who do not have the disease.
The RT-PCR test has both a high percentage of sensitivity and specificity that’s why it is still the gold standard among the diagnostic tests for Covid 19 infection. In reality, the complete name is rRT-PCR test, r is real time, Reverse transcriptase, Polymerase chain reaction. It is a NAAT- nucleic acid amplification test which detect the existence of the genetic material of the SARS-CoV 2. Its accuracy and reliability is ensured by very stringent requirements; done in highly controlled sophisticated settings, performed under aseptic conditions to avoid contamination and performed by skilled and trained personnel.
In its simplest sense, the procedure involves the so-called “thermal cycles” to make millions –hence the word amplification or multiplication, if you may-of the genetic material of the Covid 19 virus, to reach a crucial amount to produce fluorescent light in the instrument, which would indicate a positive result.
As many of patients have experienced, the ideal specimen is a nasopharyngeal swab because the spread of the virus is through droplet transmission shown in sneezing, coughing, loud talking, therefore the nose harbors the microbe. Of course, the virus may also be picked up from inanimate objects like tables, chairs on which the virus landed and is transferred unwittingly by persons who habitually touch their face, nose and eyes. A throat swab is also done because the nasopharynx continues its descent into the oropharynx- throat area- and into the laryngopharynx and unto the bronchial tree of the lungs.
The Rt-PCR test is dependable and reliable test because it can detect even low virus load, thus it would be useful in catching super spreaders who at the moment may be asymptomatic but have had a close physical encounter with a Covid 19 active patient.
ANTIGEN test is used to detect one of the 79 proteins or the surface receptors of the SARS-CoV 2 microbe which is situated on its shell or envelop. It is also called Rapid Covid 19 test and it has the advantage of being done in less stringent environment like triage areas or in border control points, with the results obtained in 30-45 minutes, in contrast to the rather long 2-3 days turnaround results of RT-PCR test.
Depending on the health status of the person who tested positive with the antigen test- meaning are there now premonitory concerning signs and symptoms of an impending full-blown Covid 19 disease or still asymptomatic- thus advice would range from immediate RT-PCR test, hospitalization , isolation and other quarantine protocols.
ANTIBODY testing, as the name implies is simply to detect the presence of antibodies mounted by the immune system of the person/patient against the antigen- found in the surface receptor of the virus. It does not have as much clinical significance and importance as those of the RT-PCR test and Antigen test in the diagnosis and prognosis (possible outcome) of Covid 19. A positive result simply means presence of antibodies probably to a previous exposure to the virus.
With the emergence of variants of viruses, not only the corona species, it’s expected there would be more diagnostic tests with high sensitivity and specificity. Meanwhile, the RT-PCR test is thankfully accurate and reliable as the alpha, beta, delta variant dance the lambada with the Peruvian lambda.
Next Week: Glossary of Terms in Infectious Diseases
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