Agreement between two diagnostic methods for COVID-19: preliminary data from a Brazilian clinical laboratory

Abstract

Objective: To investigate possible differences between laboratory profiles of symptomatic and asymptomatic patients. There are different of them available for COVID-19 diagnoses and surveillance, so this research was to evaluate the positive agreement the diagnostic methods. Methods: For symptomatic patients swab samples from nasal and oral mucosal were collected between first and second week after symptoms onset, to perform RT-PCR, blood samples were collected 7 days after to perform antibody detection test. For asymptomatic patients, only antibody detection was performed to confirm the infection. We investigated specific humoral immune response for symptomatic and asymptomatic patients and also analyzed the positivity index and kappa agreement between immunochromatographic and ELISA assays. Results: Most symptomatic patients presented negative RT-PCR with IgM and IgA detection. Symptomatic and asymptomatic patients have presented elevated IgM and IgA immunoglobulins, being this detection higher in symptomatic patients. The positivity index for immunochromatographic was higher than ELISA and there was no kappa agreement between IgM and IgA detection between these two methods. Conclusion: Symptomatic patients presented higher amounts of IgM and IgA than asymptomatic, suggesting a relation between antibody quantity and severity of disease. We verified no agreement between IgM and IgA detection, and observed higher positivity index for IMMUNO when compared to ELISA. The different kinetics may cause a variation in their detection. Also, many different virus proteins can be used as antigens in these methods, being able of altering their sensibility and specificity.