Low sensitivity of rapid tests detecting anti-CoV-2 IgG and IgM in health care workers’ serum for COVID-19 screening

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Francesca Larese Filon
Antonio Purpuri
Davide Camata
Massimo Bovenzi
Francesca Rui
Federico Ronchese
Paola De Michieli
Alessandro Marcello
Monica Poggianella
Marco Confalonieri
Francesco Salton
Paola Confalonieri
Maurizio Ruscio
Anna Belgrano
Ludovica Segat
Pierlanfranco D'Agaro
Corrado Negro


COVID-19, epidemiology, health care workers, diagnostic tests, IgG antibody


Background: the sensitivity and specificity of a rapid antibody test were investigated for the screening of healthcare workers. Methods: the serum of 389 health care workers exposed to COVID-19 patients or with symptoms, were analysed. All workers underwent monthly the screening for SARS-CoV-2 with detection of viral RNA in nasopharyngeal swabs by RT-PCR. IgG antibody detection in serum was performed by Chemiluminescence Immunoassay (CLIA) and by the Rapid test (KHB diagnostic kit for SARS CoV-2 IgM/IgG antibody after a median of 7.6 weeks (25°-75° percentiles 6.6-11.5). Results: the rapid test resulted positive in 31/132 (23.5%), 16/135 (11.8%) and 0/122 cases in COVID-19 positive individuals, in those with only SARS-CoV-2 IgG antibodies and in those negative for both tests, respectively. Sensitivity was 17.6% (CI95% 13.2-22.7) and 23.5% (CI95% 16.5-31.6), and specificity was 100% (CI95% 97-100) and 100% (CI95% 97-100) considering Rapid test vs CLIA IgG or Rapid test vs SARS-CoV-2 positive RNA detection, respectively. Conclusion: the KHB Rapid test is not suitable for the screening of workers with previous COVID-19 infection.


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