Home testing kits for COVID-19 declined in accuracy with the emergence of the omicron variant, a Dutch study published today shows.
Only one out of the three tests analysed met the World Health Organization’s (WHO) standards of at least 80% sensitivity and at least 97% specificity among individuals with symptoms.
However, writing in today’s edition of *The BMJ*, the researchers from Utrecht University say performance improved when tests used both nose and throat samples compared with nasal samples only.
While self-testing kits can support early detection and self-isolation of infectious people and reduce community transmission, there is a lack of real world evidence on the performance of nose and throat self-sampling during the omicron variant period.
The team compared the performances of three commercially available rapid antigen tests: Flowflex (Acon Laboratories), MPBio (MP Biomedicals) and Clinitest (Siemens-Healthineers), during the omicron period of the COVID-19 pandemic, based on 6,497 people aged 16 and over who had COVID-19 symptoms. All presented for testing at three public health service test sites in the Netherlands between 21 December 2021 and 10 February 2022.
All participants had a PCR test taken by a trained member of staff and they were asked to complete a rapid antigen test at home within three hours of their test site visit, followed by an online questionnaire.
When omicron was emerging and went on to account for more than 90% of infections (phase 1), nasal self-sampling was used. When the variant accounted for 995% of infections (phase 2) combined throat and nasal self-sampling was used.
The sensitivities of the three tests performed with nasal self-sampling decreased during the emergence of omicron, from 87% to 81% for Flowflex, 80% to 73% for MPBio, and 83% to 70% for Clinitest. However, the observed decline was only statistically significant for Clinitest.
When the combined test was used, the sensitivity of MPBio rose from 70% to 83% and in Clinitest from 70% to 77%, most notably in individuals who visited the test site for reasons other than to confirm a positive self-test result. However, Flowflex was not tested.
Although this is an observational study with some limitations, the authors, led by Professor Karl Moons, of the university’s Department of Epidemiology, said the omicron variant was present in at least 90% of samples in both periods.
“We found that the performance of rapid antigen tests with nasal self-sampling declined during the period omicron emerged,” they write.
“We also showed that the performance of rapid antigen tests can be improved by adding oropharyngeal to nasal self-sampling. Therefore, after proper evaluation, manufacturers of rapid antigen tests should consider extending their instructions for use to include combined oropharyngeal and nasal self-sampling.”
They conclude that people with COVID-19 symptoms can rely on a positive rapid antigen test result irrespective of SARS-CoV-2 variant dominance or method of self-sampling, while individuals should not rely entirely on a negative self-test result.
Schuit E, Venekamp RP, Jooft L et al. Diagnostic accuracy of COVID-19 rapid antigen tests with unsupervised self-sampling in people with symptoms in the omicron period: cross sectional study. *BMJ* 15 September 2022; doi: 10.1136/bmj-2022-071215
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