COVID-19 serology tests measure the amount of anti-SARS-CoV-2 antibodies that are produced in response to infection with SARS-CoV-2, the virus that causes COVID-19. COVID-19 serology tests indicate that an individual may have been exposed to the SARS-CoV-2 virus in the recent past. It is important to note that COVID-19 serology tests do not indicate an active SARS-CoV-2 infection.
COVID-19 serology testing is a valuable research tool for population-based COVID-19 studies and fundamental SARS-CoV-2 research projects. This includes vaccine trials, therapeutic drug trials, epidemiology research, and prevalence analyses. COVID-19 research in the fields of immunology, infectious disease, and coagulation may also find SARS-CoV-2 antibody tests beneficial and applicable.
The spike (S) protein and the nucleocapsid (N Protein or NP) protein domains of SARS-CoV-2 are commonly used as recombinant antigens in COVID-19 serology tests. The S protein contains a receptor binding domain (RBD) that binds the ACE2 cell surface receptor on host cells, which facilitates SARS-CoV-2 entry into the cell. The N protein is highly conserved, abundantly expressed, and functions during SARS-CoV-2 viral transcription and replication. Antibodies against the N protein show the highest sensitivity and are detected at the earliest time periods post-infection. Although antibodies to the RBD are detected at later time periods following infection, it is suggested that anti-RBD antibodies correlate with neutralization of the virus and are therefore strong indicators of immunity.
Immunoglobulin classes (IgM, IgA, and IgG) enable antibodies to recognize and bind SARS-CoV-2 antigens.
- IgM antibodies are the first to be detected following SARS-CoV-2 infection.
- IgA antibodies are detected during early stages post-infection and are found in the mucus and saliva of the respiratory epithelium and gastrointestinal system. It is further suggested that IgA antibodies function in a first line of defense against SARS-CoV-2 that may be critical for the clearance of SARS-CoV-2 from the respiratory tract.
- IgG antibodies are detected at later time periods following SARS-CoV-2 infection. IgG antibodies remain in the serum for the longest period of time, making them interesting indicators of conferred immunity.
There are different types of serological assays that measure COVID-19 antibodies: rapid diagnostic tests (RDTs), ELISA tests, and neutralization assays.
- RDTs measure qualitative data (positive or negative) in the shortest amount of time and are commonly used at the point of care. This means that RDTs indicate the presence of COVID-19 antibodies within a sample, but do not measure the precise number of antibodies detected.
- ELISA serology tests can either be qualitative or quantitative, require the use of lab equipment and reagents, and take several hours to complete. COVID-19 ELISA assays utilize recombinant SARS-CoV-2 protein domains as antigens to bind antibodies within a sample. Next, a tagged anti-human immunoglobulin antibody binds the antibody-antigen complex. Finally, the enzymatic tag enables readout of COVID-19 antibody levels (Figure 1).
- Neutralization assays quantitatively measure the ability of antibodies within a sample to neutralize live SARS-CoV-2 viruses in cell culture. This method precisely quantifies the number of antibodies required to confer protective immunity and inhibit viral replication. Neutralization assays take days to complete and require rigorous biological safety precautions.
Figure 1: COVID-19 ELISA Serology Assays
The table below summarizes the variety of COVID-19 serology tests available at DiaPharma.
|Product Name||Method||Capture Antigen||Immunoglobulin||Read-Out|
|Restalyst RAPIT COVID-19 lgM/lgG Test Kit||RDT, Lateral Flow Chromatography Immunoassay||Recombinant SARS-CoV-2 antigens||IgG, IgM||Qualitative|
|Restalyst COVID19-REAAD™ Anti-SARS-CoV-2 lgG ELISA||ELISA, Open system||Nucleocapsid protein (N Protein) and spike 1 receptor binding domain (RBD)||IgG||Qualitative and semi-quantitative data|
|Restalyst COVID19N-REAAD™ Anti-SARS-CoV-2 Nucleocapsid Protein IgG ELISA||ELISA, Open system||Nucleocapsid protein (N Protein)||IgG||Qualitative and semi-quantitative data|
|Technozyme ® anti SARS-CoV-2 RBD IgG ELISA Kit||ELISA, Open system||Receptor binding domain (RBD) of the spike protein||IgG||Quantitative|
|Technozyme ® anti SARS-CoV-2 NP IgG ELISA Kit||ELISA, Open system||Nucleocapsid protein (N Protein)||IgG||Quantitative|
|Gold Standard Diagnostics SARS-CoV-2 IgG ELISA Test Kit||ELISA, Open system||Nucleocapsid protein (N Protein)||IgG||Qualitative|