Testing for coronavirus

There are two kinds of tests used for coronavirus.

  1. Testing for the virus itself.

At present, what we use is a procedure called Polymerase Chain Reaction or PCR for identifying a component of the virus (nucleic acid).

When the component is found in the mucus sample taken from the nose and /or mouth through a swab, we conclude that the virus (SARS—COV 2) is present in the person from whom the sample was taken (positive test).

If the person is ill (symptomatic: has fever, cough, difficulty of breathing, diarrhea, etc.) and the test is positive, we say that the patient has the disease, COVID-19.

If he is well and has no symptoms (asymptomatic) but the test is positive, we say he is a carrier of the virus SARS-COV 2 that causes the disease called COVID-19.

PCR is a relatively complicated and time-consuming test to do.  It is expensive. The test kits provided by WHO cost around P5,500 per test performed. Soon there is another test that we will be able to do, using a machine called the Gene Expert which is relatively simpler and faster to do.

  1. Testing for antibodies to the virus.

When the virus infects an individual, the body defenses produce antibodies (IgG and IgM) against the virus to help fight off the virus.

At present we use rapid testing kits to test for IgG/IgM to determine if the person is producing these antibodies. The test sample is blood. The test generally becomes positive one week after the patient is infected with SARS-COV 2, whether he has developed clinical disease (COVID-19) or not.

After more than 14 days the antibodies will generally be enough for the person who has them to be rendered immune to SARS-COV 2. Immune individuals are also generally considered non-infective. They will not give the virus to other people and will not make them sick of COVID-19.

The rapid testing kit is less expensive than the PCR test. It costs between P1,000 to P1,200 per test at present.

General statement about the two kinds of tests:

  1. Neither one is perfect. They can both come out with false positive results (the test is positive even though the condition, presence of virus or antibody, is not actually there), or false negative results (the test is negative even though the condition is there).

PCR has high sensitivity (% detection of viral nucleic acid) and high specificity (% ability to differentiate SARS-COV2 from other viruses) and is the gold standard for laboratory diagnosis of the disease for clinical purposes. PCR results are however, dependent on good samples obtained through the nasopharyngeal and/or oropharyngeal swabs.

Early versions of Rapid antibody tests were saddled with low sensitivity and specificity. Newer versions however have claimed acceptably high sensitivity and specificity. At the moment, we should validate these claims before using any of the rapid tests for antibody for diagnosing immunity to the virus.

  1. Both require care in obtaining samples as no one can be sure whether the person being tested carries the virus or not.
  1. Both are expensive but PCR is 4 to 5 times more expensive than the rapid testing for antibodies.

Current Recommendations for Use of the Tests:

PCR Test

  1. For clinical testing
    1. To diagnose COVID-19 in patients who have been exposed to the virus or have traveled to an area where the virus is known to be transmitted to the community and may or may not be exhibiting symptoms compatible with the disease The former are termed Persons Under Investigation (PUI) and the latter are termed Persons Under Monitoring (PUM).
    2. To clear a patient recovering from COVID-19 for discharge
    3. To regularly monitor vital workers who are extensively exposed to COVID 19 in the course of their job (Health Care Workers)
  2. For Public Health purposes
    1. To identify carriers of the virus in selective community or group testing. Selective testing implies prioritizing vulnerable individuals such as the elderly and/or those with pre-existing significant illnesses like hypertension, diabetes, heart failure, asthma, chronic lung disease.

Rapid Antibody Test (after due validation)

  1. For clinical testing
    1. As an adjunct to the diagnosis and follow-up of COVID-19 if this is necessary.
    2. To clear a patient recovering from COVID-19 for discharge from the hospital
    3. To clear a PUI or PUM from quarantine/isolation
  2. For Public Health purposes
    1. For selective community or group testing. To identify persons who are immune from the disease for the purpose of releasing them from the expanded community quarantine to return them to economic activity. Selective testing implies prioritizing individuals performing essential services such as city hall and hospital officials and employees, policemen, essential industries and agriculture, etc.
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