COVID-19 Diagnostics : Information and guidelines for the EUI community
With reference to prevention and monitoring of the Covid19 risk, (at the moment) two main diagnostic tests are used by both the National Health Systems and private labs.
1. Swab test
this test is currently administered by health authorities within a specific protocol for detection and cure of Covid19 infection. The swab test gives the result of being actually infected or not. It’s prone to a certain extent of error (up to 30%) and this is the reason why it is administered in two (one day apart) phases. The positivity to this test can be detected in 2-3 days from the eventual beginning of the infection. This test is the basis for a diagnosis.
2. Antibody tests, divided into 2 main categories
- Rapid: this kind of test, available to private citizens, aims at detecting an immune response to the Covid19 virus. This means that it reveals whether your body has or had the infection (with or without symptoms) and the evidence is provided by the presence of specific antibodies (IgG and IgM; there are also IgA but the relevance is still to be fully understood) in a single drop of blood reacting to a specific chemical reagent. The error is around 6-14% for a false negative and 5% for a false positive. This error is quite high and therefore, this kind of test are not recommended.
- Serological test: this diagnostic test is provided by a specific technique (chemiluminenscence, the most used) applied to a venous sample of blood (the classic blood sampling test). This test, is on the average, more reliable than the rapid test but still with a detectable error margin. Same evidences of Rapid test are used in this case (IgG, IgM and/or IgA presence). In some tests, it is possible to detect the “quantity” of antibodies present in our body system.
The possible combination of results for the antibody tests are:
- IgM, IgG (eventually IgA) negative: the subject does not have antibodies and most probably he/she is not infected (unless a false negative OR the test is done within the first week from day “0” – the contagion day). It is possible that the subject has been in contact with the virus but not enough to provoke the antibody reaction;
- IgM positive and IgG (and eventually IgA) negative: the subject shows evidences of IgM antibodies and therefore, he/she may have the infection in progress. This conclusion should be verified with a “quantitative” research of antibodies (with a proper blood sample) and a swab;
- IgM and IgG (and eventually IgA) positive: the subject is, most probably, infected (disease in progress); an additional swab test is mandatory;
- IgM (and eventually IgA) negative and IgG positive: the subject shows only the “memory” antibodies – IgG. In this case he/she had the infection and recovered or is at the “end” of the healing process; Even in this case, there is a need for a swab test (two, 24 hours apart from each other) in order to confirm the recovery (both swab tests need to be negative).
Serological tests are helpful for:
- Conducting a systematic screening on population with the objective of spotting asymptomatic individuals;
- Performing an ad-hoc epidemiological investigation;
Serological tests are NOT helpful for:
- Understanding who can go to a workplace or not because:
- Errors in the tests are not a remote eventuality;
- Absence of antibodies does not exclude the infection in progress (our immune system starts the production of antibodies after one week from the infection);
- There is not enough evidence about the level of coverage to the infection provided by the antibodies in an individual;
- Diagnosing Covid19 infection: The serological tests are a sort of “still live” picture of the situation and even if they are correct (no error – false positive/negative) there is an absolute need for a swab test and a repeated testing.
In case of assumed need (e.g.: recent history of “strange” illnesses associated with Covid19-like symptoms, possible close contact with a Covid19 positive subject, etc…) you can schedule, on a voluntary basis, a serological test (with a blood sample, the rapid test is not recommended).
What do you need in order to request the test?
- A general prescription from a practitioner (for those who do not have a general practitioner provided by Italian NHS, EUI has a shortlist of general practitioners contacted in advance who will help for Covid19 related issues – prescriptions included);
- Schedule an appointment with authorized labs only (list available here);
What happens next?
In case of positive response:
- The Lab will inform the user that he/she will need to implement a self-quarantine and call the “numero verde unico regionale 800 55 60 60” in order to inform Italian Health Authorities and schedule a swab test;
- Inform the general practitioner regarding the outcome of the test;
- Inform the EUI safety_security office in order to update the EUI Medical Advisor, who is obliged to maintain sanitary surveillance for EUI members.
In case of negative response:
- Additional information: you are still under contagion risk but you did not have the infection.
- Swab test are the most reliable diagnostic for Covid19 but are provided by Italian NHS only, under specific circumstances and not upon request.
- Antibody test can give you information on a different scale of reliability:
- Rapid tests are considered – up to now – not appropriated due to their unreliability;
- Serological tests are more reliable but the information (in case of positivity) does not give you a wild card for avoiding preventive and collective measures and/;
- There is a list of authorized labs in Tuscany and some of them are aware of our peculiarities and therefore can be contacted easily;
- There is a list of general practitioners, for those who are not covered by Italian NHS, that can provide a prescription for the test”