The European Commission recommended on Wednesday the use of rapid COVID-19 antigen tests mostly on people already showing symptoms because it said the kits were deemed less accurate in detecting the virus in asymptomatic cases.
Rapid antigen kits are less precise than standard PCR (polymerase chain reaction) tests, but can offer results in a few minutes, as opposed to days, in what could prove a crucial tool in fighting large outbreaks.
“Rapid antigen tests should be used within five days after the onset of symptoms or within seven days after exposure to a confirmed COVID-19 case,” the EU executive said in a non-binding recommendation to the 27 EU governments.
It also urged states to mutually recognise rapid tests and share their testing strategies “with the aim of aligning them as much as possible”.
EU governments have differing rules for antigen tests and many are reluctant to adopt common standards, according to an internal EU document seen by Reuters.
The commission said accuracy of rapid tests in correctly spotting positive cases, an indicator known as sensitivity, increases when they are used on people up to five days after they develop symptoms and in cases with high viral load.
It added that little data was available at this stage on the performance of antigen tests in asymptomatic cases, and that manufacturers did not currently mention asymptomatic people as a target population in the instructions of their rapid kits.
The commission also urged EU governments to use only tests with at least 80% sensitivity and 97% specificity, or the ability to correctly detect people who are not infected.
It said clinical studies of antigen tests had so far shown sensitivity as little as 29% for some kits while specificity was from 80% upwards, when compared with PCR results.
The commission recommended the use of antigen tests even in asymptomatic individuals in large outbreaks, such as situations where more than 10% of tested people are expected to be positive.