Swab test for COVID-19 in Italy

The blood test for Covid-19 is used to identify a person who has been exposed to the virus and has developed specific antibodies. 

There are 2 types of tests: qualitative and quantitative. Initially most labs use the qualitative one, which just informs about presence or absence of antibodies. Amidst Coronavirus emergency, qualitative test is simpler, faster and allows to take the correct actions. At the end of the emergency, if it will be very likely more useful to switch to a quantitative test, which measures the exact concentration of IgG in the blood.

This type of test for coronavirus is currently available at some private labs and it can be done by anyone who requests it. 

This test is not useful for acute cases, such as patients who have developed symptoms, nor it can be used to rule out an infection. If you have been sneezing and can’t get tested through the official health centres, this test won’t help you either.

Serology tests are blood-based tests that can be used to identify whether people have been exposed to a particular pathogen by looking at their immune response and identifying specific antibodies. They all focus on proteins made by your immune system in response to an infection. The immune system keeps you healthy by producing antibodies, particles that destroy foreign invaders, such as viruses, by attaching to the antigens and deactivating them. 

If your blood contains antibodies that are specific to Covid-19, it means that your system has responded to its presence, thus you have been in contact with the virus.

Serology testing for SARS-CoV-2 is at increased demand in order to better quantify the number of cases of COVID-19, including those that may be asymptomatic or have recovered, and inform public health policies. 

The rapid tests for Covid-19, used to find IgM and IgG antibodies, can verify that a person has been infected, but it cannot confirm what is their current status. 

Specifically, a positive serology test for coronavirus would confirm the presence of specific antibodies, showing that the subject has been infected. However, this is not sufficient to understand if the person is still infected and contagious, or if they have overcome the disease and are no longer contagious.

A negative result, on the other hand, is even more uncertain: it may mean that the person is healthy and has not been in contact with the virus, or it could mean that the person is currently infected, but has not yet developed a detectable quantity of antibodies.

For this reason, serology tests cannot substitute the swab test used for diagnosing an ongoing infection and they cannot be used on subjects with symptoms to identify their status.

So why are these tests even done, you may ask.

From the perspective of public health authorities, policymakers, and researchers, it makes a lot of sense to get a more accurate estimate of how many people have been infected with Covid-19.

Additionally, if herd immunity were to be possible this kind of test could prove very useful to detect all those who have the antibodies and can be considered immune.

A word of caution is in order here: it’s still unclear for how long might immunity to the coronavirus last.  

Another shortcoming of the serology test is that it may show false positive results due to cross-reaction to similar viral strains, such as other common types of coronavirus. A person may result positive and be considered immune, while having actually had a different type of infection.