The state of uncertainty is one of the most distressing things for a person. Being under constant stress for two years because of the global pandemic, waiting a couple of days for the results of a covid test can be difficult. But on the other hand, rapid tests can help quickly determine the presence of infection.
What is an antigen
An antigen is a molecule foreign to the body, usually of protein origin, which can enter the human body with an infectious agent. In the body, antigens can trigger an immune response aimed at protecting the integrity of the internal environment from foreign substances. Therefore our body synthesizes particular substances – antibodies (immunoglobulins), capable of combining with antigens, binding them into an immune complex. Such immune complexes are more easily recognized and destroyed by immune cells.
Antigen tests detect the presence of proteins characteristic of the coronavirus in the sample. The test is most sensitive during the period of the most significant amount of virus in the body – usually a few days before and within 5-8 days after the onset of symptoms. Thus, a positive test result means that the patient has recently become ill and can infect others.
Coronavirus antigen test
The fundamentally new COVID-19 antigen test is an alternative to the classical PCR assay. The antigen test is performed by mouth and nasopharyngeal swab. It is highly informative in the very first days after infection.
The mucosa of the nose and throat are the entry gates for the coronavirus infection, which is transmitted by airborne droplets. During the first 5 days, the maximum concentration of the virus is reached on the mucosa. While antibody tests are powerless in the first days after infection, the antigen test is practical from the first day. The antigen test detects a specific protein in the biomaterial, which belongs to the coronavirus nucleocapsid.
The new test is more informative than standard PCR for assessing the degree of infectivity of a person. It is designed to diagnose asymptomatic carriers and patients with significant clinical symptoms.
Why express tests are needed
Specialists believe that, in addition to mass vaccination, stopping the spread of coronavirus will help rapid diagnosis to identify infected and isolate them from healthy people. Special rapid tests can help with this task.
The rapid tests show the presence or absence of lgM and lgG antibodies but not their number. Detection of lgM antibodies can indicate an ongoing infection (even if asymptomatic). Conversely, the detection of lgG antibodies may indicate a previous condition with a coronavirus and the presence of an immune response.
The accuracy of rapid tests is estimated at 80-90%, but their main advantage is speed. The result is usually ready in 15-20 minutes. Additional testing may be required for accurate confirmation.
What biomaterial is suitable for an express test for coronavirus
The most common rapid tests are those with which a few drops of blood can be used to determine the presence or absence of the human body’s immune response to contact with the virus.
To detect the SARS-CoV-2 virus antigen, express tests that use saliva as a biological material are also used.
A swab sample is taken from the nose. The result is ready within 15-30 minutes. With the rapid nasal test, you can determine COVID-19 antigen at home in the early stages of the disease.
Testers that detect coronavirus in 45 seconds. The Finnish company deep Sensing Algorithms2 received a pan-European certification for the world’s fastest tester. A person needs to exhale once – and the result is ready. However, it is not yet known how soon this super-fast tester will be available.
Where to buy an antigen test
Tests can be purchased at a pharmacy or in online stores. However, experts recommend that you undergo an examination in a medical institution or a specialized laboratory. Because there, they use proven tests, and the procedure is carried out correctly by experienced medical personnel.
Also, doctors note the accuracy of Binaxnow tests. Purchase Binax Now Antigen Test here. This Binaxnow covid-19 ag card test has been granted FDA Emergency Use Authorization for self-testing without needing to see a doctor or submit samples to a lab.
How the Binaxnow rapid test works
Binaxnow rapid tests can detect it in the body from the first days of infection. They are analogous to the PCR test but provide results within 10-15 minutes.
The Binaxnow rapid test is an immunochromatographic method (ICA) based on a reaction between a virus antigen and a corresponding antibody in biological materials (blood, saliva). If this interaction occurs, there is staining on a chromatographic strip of the test system in the area of the reference line.
When to do the antigen test
The Ministry of Health recommends whenever there are symptoms of a cold. Because they are accepted by default as potential signs of covid until a negative coronavirus test result is obtained.
How accurate are today’s rapid tests?
The most popular tests have proven themselves quite well in practice. The test itself is based on the detection of a specific virus antigen. If you follow the rules of the trial, its results can be trusted with a high degree of probability.
Producers themselves say that the percentage of accuracy of express tests is 80 % and higher (as in laboratory PCR tests).
The sensitivity indicates the ability of the test to detect the virus even in low concentrations. In medical diagnostics, this means: what percentage of infected citizens can be identified with the test.
In late May, the CDC warned that decisions should not be made to treat or isolate a person based on a single test for antibodies to SARS-CoV-2. Even “good” tests are hardly more than 90% accurate, despite the assurances of their developers. This means that:
- if 2% of the population is infected, 70% of people who test positive may be false positive;
- if only 5% of the population is infected, a false-negative result in the worst case may be half of the patients;
- if 10% of citizens are infected, a third of positive results may be false positives;
- Finally, if 30% of the population is infected, 5 out of 35 positive test results may be false.
That is, the rarer the virus is in the population, the higher the probability of antibody test error will be. According to scientists’ calculations, today, the prevalence of the virus in different categories of the population ranges from 5 to 25%. Therefore, such tests should be conducted at least twice.
Specificity indicates the ability of the test to separate the sick from the healthy, that is, to detect antibodies unique to the disease. For medical professionals, this means this: what percentage of healthy citizens can be identified with this test.
As for the specificity of the tests – and here, there are subtleties. The test must detect antibodies to SARS-CoV-2 coronavirus. But there are also other coronaviruses – the same 4 species that have co-existed with humans for many years in the form of common cold viruses. The proteins on the surface of the common cold seasonal coronaviruses and our pandemic strain may also be the same, with some exceptions.
The test would be less specific if the antibody test would “see” the entire range of antibodies to the coronavirus, including proteins common to all human coronaviruses. It would be of no use at all – the vast majority of people on the planet have probably had coronaviruses for the common cold. All you can tell from its results is that a person has recently had an acute respiratory infection caused by a coronavirus, and that’s it.
The test becomes much more specific if it focuses only on antibodies specific to a particular virus. For SARS-CoV-2, these are antibodies to the S-protein (“spike”) – the very one that clings to the ACE2 receptor of the human cell and triggers the process of introducing RNA inside it.
Antibody tests allow us to identify not those who can no longer fear contracting SARS-CoV-2 but those who need to worry about it. This problem is especially relevant in light of the growing belief among citizens that they already had a mild form of COVID-19, which was in January-February of this year. Against the background of such a belief, people are beginning to behave less responsibly, abandon antiviral protection and become a threat to those around them.
There is one more point: the tests theoretically allow us to trace the process of formation of collective immunity. A mass of factors determines the complexity of calculating this indicator:
- The sample of those who take the tests is very different in composition from the general population;
- it is not clear how long protection against coronavirus lasts and how many people develop it after illness;
- it is not clear how the virus itself changes over time, etc.
Nevertheless, the more people are tested, the more the dynamics of the coronavirus situation will be seen. And now, the analysis of these dynamics will make it possible to predict the development of the pandemic – perhaps everything is not as tragic as it may seem at first glance.