Evaluation of in-house ELISA and 11 commercial ELISA kits in the serological diagnosis of COVID-19

Introduction: ELISA-Immunoassays can complement the molecular diagnostic methods, and can be one of the important tools of sero-surveillance and vaccine evaluation. The aim of the presented study was to develop in-house ELISA and evaluate 11 commercial ELISA tests for detection of anti-SARS-CoV-2 antibodies in serum samples collected from COVID patients. Methods: In total, 237 serum samples obtained from 165 people with COVID-19 with RT-PCR confirmed SARS-CoV-2 virus infection were used for the study. The specificity of the developed in-house ELISA kit was tested using 170 serum samples obtained from patients with various bacterial and viral infections. The study used an in-house ELISA and 11 commercial ELISA kits developed by various manufacturers. Results: The presented study showed high sensitivity (81.0%) and specificity (97.2%) of the developed in-house kit in relation to the RT-PCR method. The sensitivity of the inhouse test significantly increased (98.1%) when only convalescents - persons at least 3 weeks after COVID-19 were examined. Commercial ELISA kits most frequently detected IgG antibodies (from 44.9% to 89.4%), especially in samples obtained later in the disease, and the least frequent detection of IgM antibodies (from 4.2% to 42.4%). Conclusions: All the presented ELISA kits may be used in serodiagnosis of COVID-19 however the detection of antibodies in individual tests differed quite significantly and was dependent on the period of the disease, on the class of immunoglobulins and the type of antigen used. The sensitivity of serological tests in the IgG class is clearly higher when examining samples obtained at least 2-3 weeks from the onset of clinical symptoms. Searching for IgA antibodies may be useful mainly in the early phase of the disease while IgM antibodies does not provide significant additional information. In the case of asymptomatic or mild infection, the level of antibodies is low which may be the cause problems with the correct interpretation of epidemiological surveys