The information was presented at the DGS press conference on the evolution of the covid-19 pandemic, when the Secretary of State for Health was asked about the announcement by the Portuguese Red Cross (CVP) to offer half a million tests for use in homes and schools.

António Lacerda Sales thanked CVP for the offer of tests that allow people to know their results in a short time - "between 10 and 30 minutes" - but warned that they can reveal a "false negative" when in reality the person is infected.

"In view of this high probability of negative tests, we believe that it should not be a single criterion in the evaluation," said António Lacerda Sales.

However, he acknowledged that these tests can be "an asset" in a "context of scarcity of resources, epidemiological developments and specific situations", such as outbreaks in homes or schools.

"In principle these tests also have a slightly lower sensitivity than the conventional tests we do", he explained, giving as an example situations where the patient has a low viral load and ends up having a "falsely negative test".