Why big firms shouldn’t rely on rapid tests


By Rafael Castillo M.D.


Six weeks ago, when we wrote about serious concerns on the use of rapid antibody tests (RATs) (“Rapid test kits are like toss-coin exercises,” April 21), some rebuked us for dashing the hopes of initiating a mass testing program, which was believed to be one of the major vehicles in exiting the pandemic. Although mass testing is a major factor to help us go back to as near normal a life as possible, it is not so with the use of currently available RATs. Improperly used and interpreted, RATs might even do more harm by misleading people and pushing policy-makers to make wrong decisions.

As a panelist in a webinar of a big organization, I noted a few not-so-pleasant comments in the chat box regarding my position on RATs.

When seven medical societies led by the Philippine Society of Microbiology and Infectious Diseases (PSMID) issued two weeks ago their joint advisory against the various RATs for screening purposes of manpower reporting back to work, we hoped that would convince the major proponents of RATs to put the test to proper use.

Unfortunately, up to now, we hear that several big companies are doing the tests on their employees. It has apparently not sunk in that the RAT is a very unreliable test to identify an asymptomatic but potentially infective person.

When a person tests positive in RAT, it does not mean that he’s infected. It’s just presumed that he or she might have been infected with the coronavirus at some point in the past. Antibodies are produced by the body’s immune system one to three weeks after infection.

It’s now known that after an average of 11 days, there’s no more infective virus in one who has been infected. We give it some allowance, so patients with mild new coronavirus disease (COVID-19) are advised to stay in isolation for another week after complete resolution of symptoms, and those with moderate to severe COVID-19, for another two weeks following discharge from the hospital.Cardinal dictum

We believe that it’s more logical and pragmatic to assess patients based on their clinical presentation, and counting from the time they showed symptoms, rather than basing our assessment on the results of COVID-19 tests. It follows the cardinal dictum in medicine that we should treat the patient, not the laboratory result. We’re glad that the Department of Health (DOH) has now revised its advisory of waiting for two negative tests by RT-PCR (reverse transcription polymerase chain reaction) before sending a hospitalized patient home.

The previous advisory was not pragmatic for several reasons. First, it tied up the hospital bed for another four to five days instead of making it available for another COVID-19 patient. Second, it only increased the backlog for RT-PCR testing. Third, a persistently positive RT-PCR test only caused undue anxiety in recovered patients, many of whom thought they had a reinfection or they are not cured yet, when in fact it was most likely just due to the detection of remnant viral particles which are no longer infective.

So, RT-PCR is still the gold standard for confirming diagnosis of infected persons, but not for assessing recovery from COVID-19. Going by clinical parameters is still better.

With a backlog in the number of RT-PCR tests, including the time it takes to validate the results, there is inevitable delay in the reporting. This has caused some confusion in the stats being reported daily by DOH. Hence, recently, new confirmed cases are divided into “fresh” and “late” cases depending on when the results were released to the patients.

There are questions on how to interpret this reporting. The DOH has to clarify if the tests of “late cases,” which were supposed to be released to the patients four days ago or earlier, have been validated before release, or were validated after release—hence, the late reporting. If so, then why release tests before the validation? We’ve had patients with initially positive RT-PCR results, only to be told it was negative after validation. On the other hand, if the tests of “late” cases were validated four days ago or longer, why does it take that long to report? It could not be a simple encoding problem. I’m sure there’s a good explanation, and it just has to be communicated more clearly to the public.

10,000 tests daily

Our second-liners in the 40 laboratories nationwide working feverishly to meet the demand for RT-PCR testing have to be commended, too, together with our main front-liners in various hospitals. Because some of their colleagues are either infected with COVID-19 or are quarantined due to exposure, some of these med techs are working 24/7 so they could complete more tests daily, and meet the targeted number of tests by end of June.

At the start of the pandemic, we were doing only around 300 tests daily; now, the entire system is able to do up to 10,000 tests daily. That’s something like a 3,000-percent improvement in a few months.

Reading the Facebook posts of Dr. Edsel Maurice Salvana, director of the National Institutes of Health Central Laboratory, one can empathize with all the unsung second-line heroes as they sacrifice day and night to cope with the increased demand for testing.

There’s apparently still a gap in the RT-PCR testing, which perhaps could use additional funding. And this is where the propensity for RATs can be tempered to reallocate the budget for RT-PCR testing.

If I recall right, P3.2 billion has been allocated by the government to buy RATs. We hope these RATs were not rapidly procured. Otherwise, it means we have a few millions of these test kits lying around in storage depots of various government and nongovernmental agencies.

Storage conditions of these test kits could pose a problem. Improper storage will significantly diminish the accuracy of test kits. What a waste of precious resources it would be, which could have been used more cost-effectively to ramp up our RT-PCR testing.

We understand the initial enthusiasm for RATs, as its proponents believed it could be used for mass testing. Now that experts worldwide advise us to rein in our over enthusiasm for RATs, we should reallocate the funds for it.

Epidemiological surveys

What we need is just a few thousand RAT kits monthly for epidemiological surveys to evaluate the extent of COVID-19’s spread in the population per region. It’s just like what Social Weather Stations and Pulse Asia do every quarter. By a scientific random sampling of the population, we can have an idea as to the percentage of the population that has already been infected, including many who never showed symptoms.

This can be done monthly for a few months to establish a trend, then quarterly until a vaccine becomes available. Of course, the sampling method and analysis will have to be validated and the results vetted and peer-reviewed before being released. The safeguards are important to prevent the pitfalls of subpar surveys.

Only RATs which have been validated independently by credible third parties should be used. There’s a plethora of unvalidated RATs which opportunistically joined the RAT bandwagon.I won’t be surprised if the epidemiological survey would show that the actual percentage of those who already have antibodies, suggesting previous infection, is more than 10 times what the daily DOH census tells us. The far bigger majority has gotten exposed to the virus, with their immune systems readily neutralizing the virus without any symptoms. Good for them; it means they have antibodies already to resist reinfection with the virus. We don’t know, though, how long the immunity would last.Doing regular epidemiological surveys, which would probably just entail sampling no more than 5,000 Filipinos nationwide, can let us know if we’re nearing herd immunity, which is usually attained when around 70 percent of the population is either infected or vaccinated. For sure we’re still far from that, but it’s good to know how we’re progressing. Doing research with RAT on those with previous infections may also allow us to determine how long the immunity to COVID-19 will last. Is it like measles or chicken pox, which confer life-long immunity, or is it like the seasonal flu which requires yearly vaccination to restrengthen the immunity against the virus?

So, to this day, the only known use for antibody testing in COVID-19 rests mainly in research. We see antibody testing using Elisa (enzyme-linked immunosorbent assay) as the more reliable and accurate test to measure the antibodies which can be useful in evaluating patients with previous COVID-19 infection.

Given the potential use of convalescent plasma in treating critical COVID-19 cases, Elisa antibody testing can identify people with enough antibodies who may donate their blood.

Testing for COVID-19 and for most indications can be useful and meaningful only if done on the right set of patients, at the right time, and with the right people trained in interpreting the results.

Source: https://lifestyle.inquirer.net/363966/why-big-firms-shouldnt-rely-on-rapid-tests/

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