Sensitivity of serology assay in Covid-19 diagnosis: does the antigen matter?

C Sitzia, L Pistelli, R Cardani, LV Renna, M Ranucci, M Carrara, S Borlini, P Clerici, B Rampoldi, M Cornetta, M Corsi-Romanelli

Article ID: 4021
Vol 35, Issue 3, 2021
DOI: https://doi.org/10.23812/21-163-A
Received: 9 July 2021; Accepted: 9 July 2021; Available online: 9 July 2021; Issue release: 9 July 2021

Abstract

Since the spreading of Sar-CoV-2 in March 2020, many serologic tests have been developed to identify antibody responses. Indeed, different commercial kits are directed against different antigens and could utilise different methods thereby triggering confusion and criticism. Here, we compared two Food and Drug Administration (FDA)-approved automatized assays that detect IgG responses against spike or nucleocapsid protein of Sars-Cov-2 virus in 127 subjects among healthcare workers of IRCCS Policlinico San Donato (MI), Italy. We observed different kinetics of IgG responses, demonstrating the importance of timing of sampling to correctly interpret the results both for infection diagnosis and for epidemiologic studies. We observed that Anti-N response starts earlier than Anti-S1/S2 response but also decreases earlier, affecting the sensitivity of the tests at different time points. Combining two different assays, designed against different antigens, could reduce false negative results. Finally, we observed a patient who produced anti-nucleocapsid IgG, but not anti-spike IgG. In conclusion, we investigated antibody responses in Covid-19 disease, aiming to direct clinicians and laboratory scientists to correctly interpret serologic results by always paying attention to clinical history correlation, timing of sampling, methods and antigens used, to avoid false negative results and obtain relevant epidemiologic data.


Keywords

IgG kinetics;Sars-Cov-2;antibody responses;long-term immunity;serological test


References

Supporting Agencies



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