Comparison between five different assays to detect the levels of antibodies against Sars-CoV-2 in human population

Severe acute respiratory syndrome coronavirus 2 (SARSCoV-2) is the etiological agent of Coronavirus Disease 2019 (COVID-19), rapidly spread in the current pandemic. The diagnosis of Covid 19 is based on the detection of viral RNA by molecular amplification (NAAT) in nasopharingeal swabs and virus-specific antibodies of different isotypes in the serum. IgM and IgG anti-Sars CoV-2 appear 4-7 days after the onset of symptoms but the highest level of IgM and IgG are detected after 2-3 weeks and 3-6 weeks, respectively. Serological assays are useful for the diagnosis and for epidemiological studies. To compare different methods, we measured serum antibody levels with three automated assays including Elecsys®Roche anti-SarsCov2, Abbott Sars-CoV-2 IgG and Diasorin Liason®SARS-CoV-2 S1/S2 IgG in a goup of 50 selected subjects (negative or positive for nasopharingeal swab, initial screening with Abbott serological test or previuos clinical suspect of COVID-19). A good concordance of the results (68%) was found between Roche and Diasorin assays, and between Roche and Abbott tests while the concordance between Abbott and Diasorin is lower (38%). The samples were also analyzed with other 2 non automated assays: Euroimmun Sars-CoV-2 ELISA (IgG) and Euroimmun Sars-CoV-2 ELISA (IgA). The percentage of positivity is 58% with Diasorin Liason®SARS-CoV-2 S1/S2 IgG, 42% for Abbott Sars-CoV-2 IgG, 32% for Euroimmun Sars-CoV-2 ELISA (IgA), 30% for Euroimmun Sars-CoV-2 ELISA (IgG) and 28% for Elecsys® Roche anti-SarsCov2. The concordance of ~88% and 86% was revealed between Roche test and Euroimmun (IgG), and between Roche and Euroimmun (IgA), respectively, while it reduced to 66% among Diasorin and Euroimmun (IgG) and 62% between Abbott and Euroimmune (IgG).The results in agreement with all five tests were the 34% of total selected cases. The percentage of positive specimens tested with Roche method confirmed with at least 2 other assays was 100%;this value was 93% for Euroimmun (IgG), 81% for Euroimmun (IgA), 52% for Diasorin assay and 47% for Abbott test.