During the SARS-CoV-2 coronavirus pandemic, early and reliable diagnosis is key to controlling the spread of infection. For this purpose, diagnostic tests are used, mainly including molecular and immunological tests. At the same time, rapid coronavirus cassette tests are more and more widely available on the market. Which coronavirus tests should I choose, and are they all reliable?

Coronavirus testsare necessary to determine SARS-CoV-2 coronavirus infection. The symptoms of infection are not clear-cut, and sometimes they do not appear. Therefore, for diagnostics, tests are used - mostly molecular and immunological, although there are also cassette tests.

What is coronavirus and how does the infection proceed?

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a new virus that causes COVID-19 disease. SARS-CoV-2 belongs to the coronavirus family, which also includes the SARS-CoV and MERS-CoV viruses. The SARS-CoV-2 coronavirus was identified in early January 2022 as the cause of the pneumonia epidemic in Wuhan, China. After thousands of people in China have been infected and killed, the coronavirus has spread around the world causing a pandemic.

The human-to-human transmission of the coronavirus occurs via droplets through close contact, and via surfaces contaminated with the secretion of a sick person. Hence, hand hygiene is essential in preventing coronavirus infection.

The main symptoms of the infection are:

  • fever above 38 ° C,
  • cough,
  • fatigue,
  • shortness of breath,
  • and a sore throat,
  • headache,
  • conjunctivitis,
  • loss of taste and smell
  • and gastrointestinal problems.

Symptoms appear within 14 days of exposure to the coronavirus. However, in most cases (97.5%), they begin within 11 days.

At this point, however, it should be emphasized that the symptoms of coronavirus infection vary from person to person, ranging from asymptomatic infection to severe respiratory failure and the so-called a cytokine storm. The latter are particularly vulnerable to people from high-risk groups, such as the elderly or those with diseasecoexisting (diabetes and cardiovascular diseases).

An Italian cohort study conducted in the city of Vó Euganeo by Dr. Lavezzo and colleagues found that 50-75% of people who test positive for throat swabs remain asymptomatic, while others develop mild flu-like symptoms. In contrast, only 10% of all symptomatic patients have more severe manifestations of the infection.

Coronavirus tests - which laboratory test should I choose?

In order to determine SARS-CoV-2 coronavirus infection, it is necessary to perform specialized laboratory tests, because it is not possible on the basis of clinical symptoms alone. There are currently two types of coronavirus laboratory tests in use:

  • molecular (genetic) tests
  • immunological tests (serological or antigenic)

Note that the diagnostic value of the above tests may differ.

Coronavirus Tests - Coronavirus Tests Summary [TABLE]

Molecular (genetic) testsImmunological (serological) testsCartridge tests
Research methodReal-time RT-PCRimmunoenzymatic or immunochemical methodsimmunochromatographic methods
Test materialthroat or nasopharyngeal swabvenous bloodcapillary blood taken from the finger
Detecting what?virus genetic material - RNAIgM, IgA or IgG antibodies raised against the virusIgM, IgA or IgG antibodies raised against the virus
Main purpose of the studyconfirmation of active infectionconfirmation of infectionconfirmation of infection
Place of executionlaboratorylaboratoryhome or medical point
Price of the testPLN 450-500100-220 PLNPLN 30-60
Time to wait for the resultup to 3 daysup to 3 daysfrom several minutes to 1 day

Coronavirus Tests - Molecular Testing

Molecular tests based on reverse transcription polymerase chain reaction (RT-PCR) in real time are the only ones recommended by the World He alth Organization that canconfirm active coronavirus infection.

Tests based on RT-PCR in real time rely on multiple replication in several dozen cycles of a specific fragment of the coronavirus genetic material, i.e. RNA. To do this, an enzyme called polymerase and specific pairs of primers that match the given RNA fragment of the virus are used. In the case of the SARS-CoV-2 coronavirus, it is e.g. a fragment encoding a nucleocapsid (N) or envelope (E) protein.

The next stage of the diagnostic process is the visualization of the multiplied fragment of the genetic material through special fluorescent dyes. Real-time RT-PCR, thanks to the amplification of specific fragments of the viral genetic material and the use of fluorescent dyes, is an ultra-sensitive method compared to other molecular methods. Therefore, it is able to detect even a small number of coronavirus particles in the tested biological material.

Of course, to get the most reliable results, a number of internal controls are used during the real-time RT-PCR test itself: positive, which is virus RNA, and negative, which is usually water.

It is important to know that the limitation of molecular methods is the possibility of obtaining false-negative results, which may be caused by incorrect sampling method or incorrect sampling time.

Usually, for molecular testing in asymptomatic people, material is collected from the upper respiratory tract, e.g. a nasopharyngeal swab, in which the number of coronavirus particles gradually decreases over time after infection.

Material obtained from the lower respiratory tract, such as sputum, alveolar-bronchial fluid (BAL), or bronchoaspirate, is best, although it is usually collected from people with severe symptoms of coronavirus infection.

In conclusion, molecular tests are currently the only ones recommended by the World He alth Organization to confirm active SARS-CoV-2 coronavirus infection. However, molecular tests will not answer the question of whether a person has already been infected. This is possible thanks to immunological tests.

Coronavirus Tests - Immuno Test

Coronavirus immunoassay measures the presence of immune proteins (antibodies) produced by the patient's immune system after exposure to the virus, or the presence of coronavirus proteins (antigens) in blood or biological material collected from the upper respiratory tract.

To understand what immune tests detect, it's important to know how the human immune response works. After the coronavirus enters the body, it is activatedcells producing antibodies against it in the M class (IgM). Then, over time, the IgM antibodies are gradually replaced with G-class (IgG) antibodies. In addition, the body produces class A (IgA) antibodies, which can also be used in the diagnosis of SARS-CoV-2 coronavirus. These are antibodies that are primarily important if they are measured in the secretions of the respiratory tract, because the body produces the most of them there.

It is worth noting that the time of appearance of individual antibodies differs for different pathogens. In the case of SARS-CoV-2 coronavirus infection, this time is approximately 2 weeks. And this is one of the greatest limitations of immunological research.

From the time of infection with the coronavirus to the production of specific antibodies (approximately 2 weeks), they may be absent or too low to be detected by a laboratory test. In this situation, we have a false-negative result, i.e. the person is infected with the coronavirus, but the test shows a negative result. Such results can also be obtained in immunodeficient individuals whose mechanism of antibody production is impaired.

In diagnostic laboratories, immunoenzymatic, immunochemical and immunoblotting methods are used to detect IgM, IgA and IgG antibodies against the coronavirus or possibly its antigens.

The distinct advantage of immunoassay over molecular methods is that they can identify people previously infected with SARS-CoV-2 coronavirus, even those who have been infected asymptomatically.

Nevertheless, the disadvantage of coronavirus immunoassays is the risk of obtaining false-positive results, i.e. the person is not infected with the coronavirus, but the test shows a positive result. Such a situation may take place, for example, in people who are infected with other viruses from the coronavirus family.

To sum up, serological tests detecting antibodies to the SARS-CoV-2 coronavirus can aid the diagnosis of infected people, but they are not used to confirm active cases of coronavirus infections. Immunoassays can be useful for epidemiological surveillance to identify people who have had a history of coronavirus infection.

Coronavirus Tests - Rapid Diagnostic Tests

In response to the COVID-19 pandemic and the need for quick diagnosis of infected people and the limited capacity of diagnostic laboratories, tests for the so-called coronavirus rapid diagnosis, i.e. cassette tests. Cassette tests are based on a principle similar to the principle of operation of the testspregnancy, which you can buy at a pharmacy and use immunochromatographic methods.

To perform them, you need a small amount of blood taken from your finger. The great advantage of these tests is the possibility of performing the test outside the laboratory and obtaining the result after several or several dozen minutes.

These tests are, in fact, a type of immunoassay as they test the presence of coronavirus proteins (antigens) in a sample taken from the respiratory tract or the presence of antibodies raised against the virus in the blood. However, in order for such a test to give reliable results, it requires appropriate validation, i.e. confirmation of its credibility.

Poorly chosen rapid diagnostic tests may not detect infected people (false negative results) or give false positive results in he althy people.

Based on current data, the World He alth Organization does not recommend the use of rapid diagnostic tests for detecting antibodies in patient care, due to still weak scientific evidence. However, it encourages the continuation of research work to determine their suitability for infection monitoring and epidemiological studies.

Coronavirus tests - what does the collection of research material look like?

To obtain a reliable coronavirus test result, it is very important to collect the appropriate biological material for testing. Collection for molecular testing involves obtaining a swab from the nasopharynx or throat with a special swab.

The research is not very pleasant for the person from whom the material is collected. In some cases, lower respiratory tract samples, such as sputum or BAL fluid, may be an alternative choice.

When collecting a sample from the nasopharyngeal cavity, the person taking the swab inserts the swab deeply through the patient's nose and rotates it several times for a few seconds. The procedure is performed in both nostrils.

On the other hand, if the sample is taken from the throat and the mucous membranes of the nose at the same time, the swab is first inserted deep into the throat. Then the person collecting it turns it several times and rubs it against the surface of the pharyngeal mucosa. Then the swab is inserted into both nostrils. Venous blood is taken from the elbow bend for immunological tests.

Coronavirus tests - who should do the test?

  • people with flu-like symptoms, such as high fever, persistent cough, shortness of breath
  • people who have traveled to areas with a high COVID-19 incidence
  • a person who had close contact with the person foundSARS-CoV-2 coronavirus infection
  • a person who works or visits a medical facility where people infected with coronavirus are treated

Coronavirus tests - how to interpret the results of immunological tests?

  • high concentration of IgM (or IgA) and IgG antibodies - probably active coronavirus infection, also asymptomatic. In such a case, a doctor should be consulted to confirm that he has been infected with molecular methods.
  • high concentration of IgM (or IgA) and low concentration of IgG - probably active coronavirus infection, also asymptomatic. In such a case, a doctor should be consulted to confirm that he has been infected with molecular methods.
  • low IgM (or IgA) concentration and high IgG concentration - possibly a history of coronavirus infection.
  • low IgM (or IgA) concentration and IgG concentration - probably no infection or contact with the coronavirus. However, a negative immunoassay result does not rule out active infection.

Coronavirus tests - how to interpret the results of molecular tests?

  • negative - no SARS-CoV-2 coronavirus was detected in the tested material. It means no coronavirus infection, but beware, a single negative test result does not exclude coronavirus infection, especially in highly exposed people, if the test is performed using a nasopharyngeal swab and at the beginning of infection. In this case, it may be advisable to repeat the test or collect a deeper airway specimen such as BAL.
  • undiagnostic - it means that the sample is not suitable for testing and another sample should be taken
  • inconclusive / inconclusive - it means that the result is on the border of the analytical sensitivity of the test and requires another sample after 24-48h
  • positive - SARS-CoV-2 coronavirus was detected in the tested material. This means an active coronavirus infection and requires immediate contact with the sanitary and epidemiological station

Coronavirus tests - where can it be done?

People suspected of being infected with coronavirus should report to the nearest sanitary and epidemiological station where they will be informed where they will be able to perform a refunded molecular test for coronavirus.

In addition, the Ministry of He alth is gradually updating the list of laboratories where tests for coronavirus are performed: list of COVID laboratories.

For a fee, molecular, immunological and cassette tests can be performed in commercial laboratories.

  • How to wash your hands?
  • Antibacterial gels and fluids - do they protect?against SARS-CoV-2 virus?

Category:

COVID 19