[ad_1]
To what extent can we trust a test result to highlight the status of the Covid 19 infection? A quick test Can you give false negatives? And if so, why? He answers Roberto CaudaProfessor of Infectious Diseases at the Catholic University and Director of the Gemelli Infectious Diseases Unit in Rome.
Covid Rome reservation reservation, from pharmacies to drive-ins: how, where and how much it costs
Roma, tampons: go to the salivaries “More useful also for children”
Professor, when is it correct to do a rapid antigen test and when is it necessary to do a molecular one?
«We start from an assumption. the molecular test it is the most efficient and reliable way to detect the virus during the active phase of infection, even in the absence of symptoms. Unlike molecular tests, rapid antigen tests detect the presence of the virus not through its nucleic acid (RNA) but through its proteins (antigens). The performance of the test also depends on the context in which it is used: it increases when the test is used in people with a high probability of being infected, for example, among symptomatic patients in the emergency room, and it decreases when it is used in apparently healthy people, for example a projection in a school or a gym.
Some examples? the molecular testThe so-called swab is indicated for symptomatic suspected cases with or without an epidemiological link; quarantined person if symptoms appear; close contact of the confirmed case that lives habitually or associates fragile subjects with risk of complications; detection of health professionals or personnel working in high-risk environments; asymptomatic contact in quarantine due to closure of 10 days. the rapid antigenic swab, instead, it is indicated for people with few symptoms in the absence of an epidemiological link; close contact of confirmed case that is asymptomatic (for example for schools and work), without fragile partners; asymptomatic person from risk countries; reasons for work, travel or requests not related to clinical needs “.
Why can a rapid test give negative results and a molecular test performed by the same person the next day positive?
“There can be several factors. It is possible that the patient has been positive in 24 hours, so it is necessary to wait 4-5 days before performing the test if you have been in contact with a positive. Another important element is the time with which it is processed: the sensitivity decreases significantly if the sample is not processed quickly. To be clear, it should not be settled: in that case it could give a negative value instead of a positive one. And then there’s also the swab execution – the way the nasopharyngeal swab is done – you need to take the correct amount of material. To do this you have to be careful with DIY tampons ».
Are false positives or false negatives more common?
“A false positive is more likely to come up.”
What is the difference between fast and molecular?
“The molecular highlights the RNA, allows establishing the greater or lesser amount of viral load, is more sensitive and reliable and for this it takes several days to obtain the result. The Rapido has a different method, it highlights the components of the virus that are not RNA. The advantage is that less is needed, but it is not a quantitative test and you may have less sensitive responses.
So if I am positive for Covid after 10 days of quarantine, do I necessarily have to perform a molecular test?
“Absolutely yes, precisely because of the increased reliability of the pad. Although you can stay positive for a long time with the molecular swab, it does not mean that you are still contagious. The RNA, for example, after 20 days, is no longer bound to the virus, but is present in the shed cells of the nose or throat. Therefore, as the Lazio Region indicates, after 21 days you can leave even if it is positive.
And if, on the contrary, I have been in contact with a positive, what test can I carry out: is there no risk that a negative is really positive?
“In that case, if you don’t live with people who are sick or at risk of complications, and you don’t have symptoms, you can also do a rapid test. I repeat: in percentage, the false negatives of a rapid are less than the false positives.
Last updated: 12:56
© REPRODUCTION RESERVED
[ad_2]
