Covid Tests: What They Are, When They Are Needed, How They Work, and How Much They Cost

La Covid-19 pandemic marked 2020 and is still dragging the effects of infections, virus variants and prevention and treatment actions that have seen an unprecedented global effort. Italy, among the first countries to manage infections and lockdowns, has shown great actions of health organization and great research brains united to quickly find the possibility of dealing with the epidemic.

Words like “Covid tests"and "buffer” have entered everyday language and a very large portion of the population of all ages has already had to take at least one. In fact, the swabs are the first and most effective tool for disease prevention and analysis since the first symptoms and their contribution to tracking the pandemic has been very significant.

Science and medicine have, in a short time, developed specific forms of Covid test, capable of tracking the different methods and timing of possible contagion, with appropriate differences that can be useful based on the use that is made of them.
But not everyone is yet clear about these particularities and which test to request based on symptoms or cases of possible contagion.

Among the Covid tests that will be examined, some are now known and widespread. It is possible to request their execution at the analysis laboratories of the Multi-specialist Center Medi in Castellammare di Stabia, whom we asked to illustrate the main characteristics and differences, How do they work and what levels of effectiveness do they have?. In fact, it is important to clarify some tests, as they are still little used.

Covid molecular swab

When referring to a molecular test, now, the thought that imposes itself is that of the swab. This type of test is now very widespread and has become one of the symbols of this period of pandemic: it is the most widespread and safe Covid test for recognizing the presence of the virus in the body.

The swab is inserted into the nasal cavities of the person undergoing the test and has the aim of recognizing the genetic material of the virus itself in the nasopharyngeal mucosa. If this material is recognized by the molecular tests with a reaction to reverse polymerase chain, it means that the person is positive for Sars-cov-2 virus.

It is certainly a reliable tool, but all in all slow (from hours to a couple of days are needed for the results), without considering the exposure to the risk of contagion of the operator who carries out the swab itself.

The molecular test is useful to confirm any quick swabs or to assess the status of quarantined subjects (both in the case they begin to show symptoms and in the case in which it is necessary to confirm their recovery). The test can be carried out at clinical laboratories and costs may vary from region to region.

Covid Antigen Test

The molecular test therefore searches for the genetic material that constitutes the virus. Instead, the antigen test has the task of identifying viral proteins (antigens) specific. The method used for the recognition of proteins is the same as the molecular test: a nasopharyngeal swab (similar to a cotton swab with a longer shaft) but the test gives, in these cases, a quicker response.

We are talking about a wait of just fifteen minutes but the reliability of the test, on the other hand, is reduced compared to a molecular swab: it is therefore advisable to confirm an antigen test (now commonly known as "quick swab”) with a second molecular test, to avoid the risk of false negatives.

Given the speed of the test, however, it is recommended thatantigen test when necessary for school or work (due to its speed) or, again, in case of mild symptoms if there has been no close contact with positive subjects (symptomatic or asymptomatic).

Covid Serological Test

Unlike the two previous tests, the serological test It does not look for genetic or antigenic components of the virus, but for antibodies produced by the body in response to the coronavirus. If present, they testify to the body's contact with the virus itself, but they cannot say anything about a possible ongoing infection. In fact, once the infection has occurred, the body takes a few days to be able to mobilize the right antibodies, which remain in circulation in the blood even a long time after the virus has been expelled.

In this sense, serological tests have no diagnostic value: being negative to a serological test could mean – in some cases, for example – having an ongoing infection and not having yet produced the right antibodies (the virus could still be in the incubation phase); on the contrary, a high antibody count does not help to recognize when you have come into contact with the virus. However, it is a very useful test for studying the epidemic itself, and for analyzing its progress in more or less large communities.

There are three types of serological tests, the costs of which – at clinical analysis laboratories – vary from region to region:

• Rapid serological test or qualitative: the analysis of a single drop of blood is sufficient to verify – in just twenty minutes – whether the body has produced antibodies against the coronavirus.
• Quantitative serological test: it is based on a venous blood sample; the blood is analyzed to trace IgG and IgM antibodies, that is, the first to appear in case of infection. The reliability is around 98%. If the IgM immunoglobulins are positive, you will be dealing with a recent infection. Otherwise (positivity of the IgG antibodies and IgM negativity), the infection has now passed; in this last case we can speak of a potential immunization of the subject.
• Quantitative spike test: this is a serological test aimed at finding active antibodies against the S protein (Spike) of the SARS-cov-2 virus. This latter test is particularly suitable for verifying the immunization of the subject following recovery from a coronavirus infection or completion of the vaccination cycle against the coronavirus.
  Again, the test is based on the analysis of venous blood, which is subjected to chemiluminescence (a test with a specificity of 99,6% and sensitivity of 100%). This is a test that is worth carrying out two weeks after completing the vaccination cycle or three weeks after the Covid-19 infection: in both cases, it will be possible to verify the presence in the blood of antibodies capable of recognising and attacking the Spike protein that the coronavirus uses to attack cells: once this protein is neutralized, the virus will have no way of infecting the host organism.
  Being therefore more targeted and specific than the two previous serological tests, it Spike test it proves more suitable for monitoring one's immune response to the virus over time, following recovery or vaccination.

Covid saliva tests

Recently, tests similar to molecular and antigen tests have been developed, which, however, do not depend on a nasopharyngeal swab but are based on the analysis of a saliva sample. This is therefore a less invasive test than the classic swab or venous sampling and, for this reason, could prove to be a fundamental tool for rapid screening of entire communities. However, there are some data to keep in mind.

Il molecular salivary test, in fact, has waiting times of about an hour and is extremely suitable only in some circumstances: for example, to confirm the validity of a positive antigen test. The saliva antigen test has, as a contraindication, the need for a sample to be taken at specific analysis laboratories: therefore, it is not suitable for rapid screening.

Covid Prevention and Testing

The strategy for the prevention and containment of the spread of pandemic da Covid-19 It is based on the so-called 3 T: test (test), trace (tracing), treat (treat). It is thus understood that the first step (that of the tests to be administered to the population) is fundamental to continue with the work of recognition and treatment of the positive cases found.

Over time, different types of tests have been developed and others are still being developed, to ensure ever greater speed in recognizing positive subjects, so as to nip any potential outbreak in the bud. For this reason, tests are confirmed as the main tool for preventing the spread of Covid infection.