NEGATIVE OR POSITIVE: All about the COVID-19 tests

Published September 10, 2020, 7:57 AM

by Noreen Jazul

  • The COVID testing methods now being done in PH

  • How is each test conducted

  • The cost of the tests

  • When will you get the results

  • When is best time to have a test

  • Other testing methods used in other countries

“Test, test, test.”

As a major strategy in the battle against the coronavirus disease, testing has become the standard procedure to prevent the entry of a carrier of the virus into the country, cities, and even in special events. Testing is also the same strategy to prevent the spread of the virus in smaller communities.

Although testing would not be the only factor to stop the pandemic, it gives information on where the infections are coming from, and, it will give medical authorities the opportunity to “interrupt the transmission of the disease,” explained Baguio City Epidemiology and Surveillance Unit (CESU) head Dr. Donnabel Panes.

“In testing patients we will be able to identify where the patient got the virus and who are those who he or she might have infected. In that way, we can interrupt the transmission of the disease by isolating those who turned out to be positive and those who were exposed,” Panes told Manila Bulletin in an interview.

There are several types of COVID-19 tests used in other countries, each one developed to detect the carrier of the virus.

In the Philippines, there are two types of tests currently being used: the RT-PCR (real-time polymerase chain reaction) test and the Rapid Antibody test.

Types of tests

Currently, one of the diagnostic tests which is used for detecting COVID-19 is the RT-PCR (real-time polymerase chain reaction test), a molecular test. The other diagnostic tests used in other countries are the saliva test and the antigen test.

RT-PCR, the gold standard

The RT-PCR is considered the “gold standard” for COVID-19 testing by the DOH and the US Centers for Disease Control and Prevention (CDC).

Dr. Sam Bartolo, an Infectious Disease Expert at St. Louis University Hospital of the Sacred Heart in Baguio City, said the RT-PCR is also the “test of choice” of medical experts because of its accuracy.

(JANSEN ROMERO / MANILA BULLETIN)

“Based on accuracy, [the best] is still the RT-PCR, kasi (because) it will detect the RNA (Ribonucleic acid) of the virus,” Bartolo told The Manila Bulletin in an interview.

The FDA had also stated in its website that RT-PCR tests are “highly accurate,” and does not need to be repeated.

How test is done

In the RT-PCR test, samples are taken through nasal or throat swab. Ideally, Bartolo said both oropharyngeal (throat) and nasopharyngeal (nasal) swabs should be done for more accurate results.

Dr. Bartolo said the RT-PCR test, compared to the antibody test, has “higher accuracy, sensitivity, and specificity.”

But it is quite expensive. In private hospitals, Bartolo said an RT-PCR test would cost around P4,300. “In government facilities, you don’t pay as much,” she added.

If the RT-PCR test is done in a government facility, and the patient has no PhilHealth, Bartolo said the cost would be around P3,600.

For tests done in a private institution but sent to a government laboratory for analysis,a patient will need to pay a handling fee of around P600, for those with PhilHealth, and P1,000 for those without PhilHealth.

At a Philippine Red Cross (PRC) laboratory, an RT-PCTR test costs about P4,000.

Bartolo said the RT-PCR is a “little pricey” than other tests because it requires different equipment, a Biosafety Level 2 laboratory, and expert personnel who will run the tests.

Health workers who perform the RT-PCR test must wear full personal protective equipment, according to Bartolo. WHO said a full PPE consists of face protection, goggles and mask or face shield, gloves, gown or coverall, head cover, rubber boots.

The US FDA said samples taken in clinics, hospitals without laboratories, or drive thru testing centers, must be put and sealed at a “sterile container.”

While on transport to the laboratories, the samples must be kept at storage temperature of 2-8°C, according to the WHO.

If there will be delays in the transport, WHO said specimens may be frozen to “- 20°C or ideally -70°C and shipped on dry ice.”

When is RT-PCR test free?

RT-PCR tests done by the government for surveillance purposes, however, are free of charge, according to Dr. Panes.

Dr. Panes said individuals “under priority testing” (based on DOH’s Administrative Order (AO) 2020-00258A) can also avail of free testing. These include “suspect cases, individuals with travel history and exposure (whether symptomatic or asymptomatic), and healthcare workers with possible exposure (whether symptomatic or asymptomatic).”

Subsidized by PhilHealth

“Other [RT-PCR] tests are either paid or subsidized by the Philippine Health Insurance Corporation (PHIC),” Panes said.

Results

Bartolo said patients can get results of their RT-PCR test within one to two days if done in a private laboratory, and about two to five days if done in a government facility, depending on the number of tests being run.

Rapid antibody test

An antibody test or serology test is used to detect whether a person has developed antibodies against a specific virus.

This test is conducted through a blood sample which is either taken from the finger through a simple prick of a needle, or through the drawing of blood from a vein.

(JANSEN ROMERO / MANILA BULLETIN)

Bartolo said there are three methods which antibody tests are done: by use of the rapid kit, CLIA method (Chemiluminescence Enzyme Immunoassays), ELISA method (Enzyme-linked immunosorbent assay).

“The rapid kit is the point of care test because it can be done right then and there. You just need a few drops of blood from the patient, which is dropped into the well of the kit and mixed with the reagent,” Barotlo said.

Antibody tests using rapid kits takes 15 to 20 minutes to perform, Bartolo added.

“The CLIA and the ELISA on the other hand (some labs use either method) is a laboratory based test. You have to extract the blood of a patient and run it in the lab,” she explained.

What this test will show

There are many opinions on the use of the Rapid Test.

The DOH also has earlier discouraged the use of rapid antibody test for screening, citing its “low sensitive and high false-negative test rates” and “uncertainties to its connection to immunity.”

Bartolo said she supports calls to discontinue the use of the rapid antibody tests for screening purpose. Health experts have expressed opposition in the use of anti-rapid body test kits, particularly in workplaces.

Dr. Antonio Dans of the Philippine Society of General Internal Medicine in an online forum last August 4, said use of rapid antibody test should be stopped.

(JANSEN ROMERO / MANILA BULLETIN)

“The use of rapid antibody tests should be stopped. I think, among all countries, we are the only ones still using it,” said Dans said in Pilipino. “It does not detect the virus but the antibody,” he added.

The infectious disease expert said that a serology test, which is the Rapid test, would only show a positive test result days after the infection.

If you use it as screening, high chance that it will turn out negative even if the patient is positive. So you’re going to give patients a false sense of security, she said.

She added that while rapid antibody tests are the cheapest and has the fastest turnaround time at 15 minutes, it is also the least accurate.

She said the Rapid test can be used for “retrospective diagnosis” of those who are recovering or who have recovered from COVID-19.

In the US, the FDA has said that the result of an antibody test will show whether a person has been infected by COVID-19 in the past days or weeks. The result is not to be taken to diagnose active coronavirus infection.

Cost

Anti-body rapid tests are not covered by PhilHealth, according to Bartolo.

A CLIA antibody test costs around P1,500 to P2,000 both in private and government facilities, according to Bartolo.

“With regards the rapid kits price, I do not know how much they really cost because in my experience, those kits were usually donated to the hospitals,” she said.

“But some private sectors have been selling them for around P1,500,” she added.

The other tests for COVID-19 which are now being studied by Philippine medical authorities are the saliva test and the antigen test.

Saliva test

The Saliva test is a new type of diagnostic test which uses a tube to collect the spit.

The FDA said this alternative method of testing “may be more comfortable for some people and may be safer for health care workers who can stand at a distance during the sample collection.”

Earlier this month, the Yale School of Public Health’s saliva-based test SalivaDirect was granted an “emergency use authorization” by the US FDA.

In the Yale website, SalivaDirect is a protocol that is “simpler, less expensive, and less invasive” than the traditional swab test.

“Results so far have found that SalivaDirect is highly sensitive and yields similar outcomes as NP swabbing,” Yale reported.

Not a kit but a protocol

FDA clarified that SalivaDirect is not a kit, but rather a protocol, offered to laboratories by Yale researchers.

“The designated laboratories could follow the protocol to obtain the required components and perform the test in their lab according to Yale’s instructions for use,” FDA explained.

Yale researches said they expect labs to charge $10 per sample.

Like other diagnostic tests, saliva tests also show whether a patient has COVID-19 by detecting the genetic material of the Sars-COv-2 virus in samples.

“The laboratory already analyzes patient samples for an RNA signature unique to that of SARS-CoV-2, the virus that causes COVID-19,” Yale researches said.

What makes saliva tests different, specifically Saliva Direct, is that it “doesn’t require extracting the nucleic acid from samples before testing,” which is done in RT-PCR tests.

“Nucleic acid extraction is time-consuming and expensive, and there have been worldwide shortages of the supplies needed to do it,” Yale researches explained.

Meanwhile, the Philippines’ Research Institute for Tropical Medicine (RITM) said it is still studying whether this type of test can detect Sars-COv-2.

Antigen test

While the RT-PCR test detects the genetic material of the Sars-COv-2 virus, the antigen test looks for “specific proteins” on the virus’ surface.

This test is usually done “earlier in the disease” according to Bartolo, unlike the rapid antibody test which is usually done on the “later part of the disease.”

Compared with the RT-PCR test, the rapid antigen test has a faster turnaround time. It’s usually read 15 minutes to one hour, but releasing time may take up to two days, Bartolo said.

A taxi driver (R) gets tested by health workers (L) for coronavirus COVID-19 at a makeshift testing station in a carpark in Hong Kong on July 19, 2020. - The deadly coronavirus is spreading out of control in Hong Kong with a record 100 new cases confirmed, the finance hub's leader said as she tightened social distancing measures to tackle the sudden surge in infections. (Photo by ISAAC LAWRENCE / AFP)
(Photo by ISAAC LAWRENCE / AFP)

In terms of accuracy, the US FDA said that positive results shown by antigen test are “usually highly accurate.”

However, the FDA said patients who tested negative in an antigen test but have symptoms “may need” to take a molecular test.

FDA explained that antigen tests cannot “definitively rule out active coronavirus infection.”

“Antigen tests are more likely to miss an active coronavirus infection compared to molecular tests,” it said.

This was echoed by Bartolo saying antigen’s accuracy is “less than” the RT-PCR’s.

Testing is about timing

The two doctors agree that timing is important when conducting tests.

“It would depend on the stage of the disease. A patient should seek the opinion of a doctor on which test he or she should take because the doctor can determine which stage of the disease the patient’s symptoms show,” Dr. Bartolo said.

Barolo said the best time to get tested is when a patient is already symptomatic.

 
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