CLIA immunoassay as an alternative and accurate method to detect Sars-Cov-2 antigen compared to ELISA.

Background: COVID-19 has caused moderately severe infections in humans over the past few years, leading to >759 million confirmed cases. This situation highlights an urgent need to develop accurate diagnostic tests to monitor infectious disease and to adopt alternative methods such as CLIA to achieve low detection levels of proteins on diagnostic platforms.

Objectives: Develop in-house immunoassay for ELISA and CLIA to diagnose COVID-19.

Methods: 200 nasopharyngeal samples were collected using swabs, placed in tubes with 3 mL of PBS. 1 mL from each sample was used to perform qRT-PCR and was considered positive in samples with CT < 38. The remaining volume was used for in-house sandwich immunoassay ELISA and CLIA.

Results: The results showed that CLIA was able to detect active disease in samples containing N protein concentrations greater than 16 ng/mL, with a sensitivity of 90 % and specificity of 94.5 %, and an area under the ROC curve (AUROC) of 0.943 (95 % CI: 0.909-0.977). ELISA showed an AUROC = 0.709 (95 % CI: 0.639-0.778), with a sensitivity of 54.4 % and specificity of 87.2 %.

Conclusions: The CLIA results in this study outperformed the traditional ELISA and proved to be a suitable platform for monitoring the progression of disease stages, including the diagnosis of active COVID-19 infection.