Rapid Tests: Essential or Useless?
It has become well-known that COVID-19 caused by the novel coronavirus (SARS-CoV-2) has turned into a pandemic affecting the whole world. This has made all countries to face a critical situation has never seen before. As it happened regarding many “hot topics”, unreliable content has spread through the internet quickly – including posts about denying the real danger or increasing the panic, fake news, quotes and facts taken out of their original context to give then an entirely different meaning.
A special category of these sorts of unreliable information consists of articles trying to prove that tests – especially rapid assays – are useless and cause more harm than good. This page, which appeared on one of the most reliable Hungarian news portals has been read and shared by a lot of people. It is no doubt that the author’s original intent was benevolent – however, the article contained some inaccurate and unproven information. Although it has not been the only page that has been issued somewhat misleading content, we think it is worth reacting on the particular article. Hvg.hu is generally considered to be a relevant source of news; the fact they posted an article of certain pieces of inaccurate information shows how easy it is for other, less known pages to make the same mistake, too.
Tests for the Masses
Firstly, how does the test go?
One possibility is to detect the genetic material (the RNA) of the virus. The specimen can be collected using several types of human cells (e.g. the saliva). The RNA of the virus has to be isolated, and a detectable amount of genetic material can be produced by a reaction called PCR (Polymerase Chain Reaction). This is a highly reliable method for examining whether the virus is present in the body.
Rapid tests, on the other hand, detect the virus in an indirect way. These examine whether the antibodies produced by the human immune system to the novel coronavirus are present. These are called immunochromatography tests or serological tests, too; the rapid test name refers to the fact that the result can be received in about 15 minutes.
It has been reported from several countries (e.g. Great Britain) that having examined several wide-spread rapid tests it turned out that they had been not very reliable. There even were tests which, using them on people showing the typical symptoms of COVID-19, were able to identify the virus infection with a mere chance of 50%!
- the companies manufacturing serological tests are unable to serve the current world market of colossal size, therefore there have been firms beginning to produce rapid tests due to SARS-CoV-2 with little to no experience on the field of immunochromatography
- the critical situation has made plenty of countries to speed up the process of licensing
- certain people hope if someone needs the tests urgently, they will not browse through the necessary documentation thoroughly – or will not ask for them at all.
That said, it would be surprising if the majority of the tests were actually able to pass a thorough performance examination!
Keeping all these things in mind, it is worth focusing not only the price of the product (and maybe the fast delivery, too), but also checking whether the documentation is valid. (E.g. Does the manufacturer have an authorized representative in the EU? Is it allowed legally to sell the product in the EU?) Asking for a clinical trial confirming the efficacy of the test, and checking whether it is registered by an authorized body are important, too. All this information must be shown on the packaging or in the user’s manual, or must be provided by the manufacturer when (and not if!) it is asked for.
Another thing one should pay attention to is the Internet itself. Does the manufacturer have a home page at all? If so, is it said how long the company has been developing and manufacturing similar products? It is a safe assumption that companies having been on the field of serological tests have more reliable products than those from which there is no information on the Internet. The article linked above explained that the Hungarian National Ambulance Service (OMSZ) started to use two types of serological tests manufactured by two separate companies: Anhui Deep Blue Medical Technology and Hangzhou Clongene Biotech . A quick search reveals that these companies were established in 2010 and 2004 respectively; both of them had been renowned for their serological products before the SARS-CoV-2 outbreak.
There is one more thing to point out. Regardless of the COVID-19 situation, negative news spread much more quickly and people can remember to them longer. The information about withdrawing masks and tests had bigger impact on the Internet society than the fact that thereware 160,000 tests made in Germany, and the mortality rate is very low in that country in spite of the number of infected people..
Tests for Jests?
There was a quote, said to be a part of an internal correspondence of the Hungarian Academy of Sciences (MTA) Research Centre for Natural Sciences. It said: rapid tests “are totally useless, because the antibodies appear in the blood mostly after the infection has run its course. In fact, they can be found only in the blood of those who have already healed.”
The original context of the quote is not known, but the statement is, in itself, wholly wrong.
Most rapid tests available on the market detect two antibodies which are produced especially against SARS-CoV-2. These are called immunoglobulin M and immunoglobulin G, commonly abbreviated as IgM and IgG respectively. IgM appears in a detectable amount on the 5–8th day of the infection. It is present for weeks, but usually cannot be detected after 4 weeks. IgG appears later, 2 weeks after the infection. It peaks at the end of the first month, then its amount falls. However, it is detectable for at least several months after the infection. The exact values are not known yet; partly because everyone responds differently to the infection, partly because there are not enough data available yet. An article of NewScientist appears to be the most cautious: it says IgM appears on the 10th day of the infection . In contract, the American Food and Drug Administration (FDA) guideline compiled for healthcare workers says that IgG can be detected on the 7-10th day of the infection.
According to this information, rapid tests are indeed unable to detect the virus in the early phase of the infection. However, they are able to do so in most cases after the characteristic symptoms of COVID-19 have appeared, and they most likely detect the infection in the late phase of the disease.
That said, “useless” can refer to one fact: using a rapid test alone is indeed insufficient to determine whether someone has become infected recently.
On the other hand, those who have the virus can be spread the infection for a month even if they are symptomless! Rapid tests are thus of great help in identifying a lot of infected people. Isolating them is the best way to prevent them infecting others, which means the spread of the novel coronavirus becomes slower.
It is worth pointing out that many of the institutions offering rapid testing emphasize it that those whose tests show a positive IgM result should spend the next 2 weeks in isolation – or, if the symptoms are severe, in hospital.
There is another important aspect of rapid testing. It is the best way of identifying those people who have already fought off the disease. (At that time, only IgG is present in their blood; IgM is not.) People with a positive IgG test (and a negative IgM one) may be infectious for another 2 weeks. After that period, they are safe: neither they can infect others nor they are in danger anymore. (Even if they catch SARS-CoV-2 again, they can fight off the disease in very short time, possibly without any symptoms.) The importance of this is tremendous regarding companies and institutions of big manpower. Using rapid tests, it is easy to decide who can return to work safely, which will be a vital piece of information in the future, when the pandemic is dying away (or when its second wave breaks out).
Who Should Have the Rapid Test Taken?
Since high temperature is one of the most known symptoms of COVID-19, plenty of people thinks only those are to be tested who have fewer. The same misunderstanding appeared in the article of hvg.hu (though the same unknown source): “antibodies are present in a detectable amount when the body responds with raising the temperature for the disease. Therefore, those should use the test who have flu-like symptoms.” In fact, most institutions offering rapid testing – including Kelen Kórház, Róbert Kórház, and Prémium Egészségpénztár (two hospitals and a health fund institution) – emphasizing the opposite. It should be, actually, self-explanatory that in case of severe symptoms caused by COVID-19 the highest priority is to treat the symptoms themselves. This can happen at home (people are doing so in case of other illnesses like flu, aren’t they?), or, if the situation is critical, in hospital environment.
Most institutions (including those linked above) post their recommendations, too. These usually include the following: You should have the test taken if
- the chance of having contacted an infected person recently is high
- there has been an illness of flu-like symptoms in your family
- you experience the typical but mild symptoms of COVID-19
- you have been to abroad and/or any place where the risk of infection has been high
- you think that you have already fought off the infection.
Again, it must be noted it is worth for large companies and institutions having their workers tested. This is a quick and efficient way to check whether the virus is present at the workplace. For them, the financial impact of testing is tremendous (may be the difference between closing down the company or not!), and it makes possible to prevent the spreading of the virus in case social isolation is impossible due to the nature of the work.
„It’s Only a Little Needle and I Know Everything… Don’t I?”
Rapid tests are sold for professional use only! They cannot be sold directly to public people!
Rapid tests count as In Vitro Diagnostic (IVD) medical devices. The regulation applied for professional use devices is greatly different to that of non-professional use devices. The registration and licensing process of the latter one is much more complicated and it takes at least 6 months. That said, currently there are no home-use rapid tests legally available on the market – even if certain webshops say the opposite! Moreover, in Hungary only licensed institutions can perform immunochromatography tests. The testing itself need not take place at the institution, though, but the environmental safety of collecting specimen and the epidemic health conditions of the health workers must be ensured.
Indeed, specimen can be collected from finger prick, too (in the same way as it is done for blood type tests). However, many institutions use venous blood. From this specimen the plasma can be isolated, which enables later examinations, too. Thus, using venous blood provides more reliable results.
False Negatives = False Hopes?
The most frequent issue mentioned in connection with rapid tests is that negative results do not essentially mean that somebody is not infected.
Indeed, besides SARS-CoV-2 is not present in the body, the lack of IgM and IgG can mean two other things.
- In the very early phase of the infection it is possible that IgM has not been produced in a detectable amount yet
- The tests subject has already been infected but their immune system does not produce a detectable amount of antibody for some reason.
In fact, those institutions which offer rapid testing – for example, Kelen Kórház and Róbert Kórház – clearly explain this on their webpages. They also emphasize that the test should be repeated in the future if the chance for being infected is high. Moreover, it must be said that rapid tests alone can never be the basis of a diagnosis – doctors have to diagnose the patients through thorough examination.
The related information should be included in the user’s manual of the rapid tests, too. The corresponding documentation of Clungene COVID-19 IgM/IgG Rapid Test Cassette, for example, says the following:
“If symptoms persist and the result from the COVID-19 IgG/IgM Rapid Test Cassette is negative, it is recommended to re-sample the patient a few days later or test with an alternative test device. A negative result can occur if the quantity of antibodies for the SARS-CoV-2 virus present in the specimen is below the detection limit of the assay…”
Giving false hopes are definitely out of question – both the manufacturers both the related institutions explain the limitations of rapid testing.
PCR is the Best – Forget the Rest?
It must be cleared: no serological test can perform better than a PCR test. In an ideal world rapid tests would be unnecessary indeed. The reality is, on the other hand, different.
Firstly, PCR tests are very expensive. The instrument used for testing costs ten thousands of Euros, the essential tools, materials and the tests themselves are not cheap either. In several countries – Hungary included – there are few institutions capable and licensed for performing PCR tests. The process is time consuming (alone the chain reaction lasts for an hour), the steps of the protocol are complicated, the chance of mistakes is relatively high. During the same amount of time much fewer PCR tests can be taken than rapid tests nationwide.
Although PCR tests can detect the virus earlier than rapid tests, they are still not able to detect the infection in its beginning phase. Collecting the specimen is a critical step, too. It can occur that no cell including the virus becomes collected at all. Therefore, even PCR tests are not 100% reliable.
Finally, since PCR tests detect the virus itself, they provide no information whether someone has already fought off the infection or has not been infected yet.
In the future, the most important advantage of serological tests is being able to find people who are IgG positive and IgM negative. Most likely, these people have already fought off COVID-19 (or they were symptomless) – the presence of IgG, which means they are immune, shows this. Passive immunization has been used in the medical practice for a long time. During this process the blood of people who have already recovered can be taken (though blood donation or plasmapheresis), processed for extracting their antibodies. These may be used for patients of severe condition in the form “gamma globulin” or other IgG preparation. Moreover, since these IgG positive people are most likely immune to the disease, they can be the key for finishing the financial and social crisis we have to face presently.
Summarizing the conclusions, it is true that rapid tests are not impeccable, they can be used only by professionals (just like PCR tests), and if they are from dubious sources, the lack of their reliability can even cause unnecessary risks. However, they are able to identify the virus from the second week of the infection, which is especially important if there are large amounts of people to test. Since they can detect the virus in a considerable time-range of the infection (and after fighting off the infection, too), rapid tests can be important tools for subduing the world-wide pandemic.