Single antigen tests detect just half of cases in asymptomatic patients

Single antigen tests detect just half of cases in asymptomatic patients

The HSE working group say antigen testing may be suitable for certain settings but warn that their findings should not be extrapolated to justify the use of home-testing kits.

Single antigen tests are not recommended for use by asymptomatic people, as a “significant proportion” of infections will be missed, a HSE review has found.

Using one test with asymptomatic people, just 52% of positive cases were detected, compared to a PCR test.

The report from the HSE Covid-19 antigen testing working group shows the working group evaluated seven antigen tests including six lateral flow tests and one microfluidic device with a reader.

The use of antigen tests has been hotly contested in Ireland despite being in wider use in other European countries.

Working group's recommendations

This working group has now made five recommendations.

They state: “For the purposes of asymptomatic screening, a single, stand-alone antigen diagnostic test is not recommended, as a significant proportion of people who are infected, and infectious to others will not be detected.” 

However it showed 80% sensitivity in picking up symptomatic people, and other tests were found to be equally or more sensitive in this case also. They found that as people with Covid-19 are infectious even when they have a low level of the virus which would not be picked up by antigen tests, that "testing systems that detect virus at the lowest possible level are generally preferred". 

Antigen test in parallel with PCR test

They recommend that the tests are suitable for symptomatic people in parallel with PCR testing, especially with groups where following up after a time-lag with a PCR result might be challenging.

They also recommended one test which could be used with “supervised self-collected nasal samples”, saying this is comparable to the situation in meat plants where antigen tests were used and backed up with PCR testing.

And they recommend that anyone setting up antigen testing programmes should supervise “clinical governance and quality management of all aspects of sampling and analysis”.

Wide variation in sensitivity

The report also states that there is wide variation in sensitivity among the tests, and recommendations around use of any particular test cannot be applied to all antigen tests.

However they noted that, despite this, the antigen tests may be more suitable for certain settings due to having a faster turnaround.

They also warn the findings should not be extrapolated to justify the use of home-testing with antigen kits.

• The 43-page report is available as a PDF file here on the HSE website. 

 

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