COVID-19 testing in Las Vegas

Types of Antibody Testing for COVID-19

Antibody testing can be classified broadly as detecting whether in-binding or neutralizing antibodies.

• Binding antibody detection: These tests employ pure proteins of SARS-CoV-2, not living viruses, and may be done in facilities with lower biosafety levels (e.g., BSL-2). Individual antibody types, such as IgG, IgM, and IgA, can be distinguished using particular reagents. IgG antibodies and SARS-CoV-2 IgM might be found at the same time. However, whereas IgM is most effective for diagnosing recent infection, it frequently remains undetectable for weeks or even months after infection; IgG, on the other hand, is usually detectable for extended periods.

IgA is vital for mucosal immunity and may be found in mucous secretions such as saliva and blood; however, its role in this condition is unknown. Based on their complexity, several binding antibody tests can be completed quickly in the field or a laboratory environment.

There are two types of tests that detect binding antibodies.

• In point-of-care tests, the results of a test are obtained within minutes rather than hours after the sample is collected. IgG, IgM, or total antibodies can be detected in fingerstick whole blood by antibody POC tests, generally using lateral flow devices.
• Antibodies can be detected in serum, plasma, whole blood, dried blood spots, or by lateral flow, ELISA, and chemiluminescent immunoassays (CIAs), which are often performed by trained laboratory scientists using specialized instruments. IgG and IgM antibodies can be detected separately, or total antibodies (Ig) can be detected. Some tests detect antibodies against both immunodominant proteins (multiplex assays), while others detect antibodies only against the S or N proteins.
• Neutralizing antibody detection assays assess antibodies’ capacity to prevent SARS-CoV-2 infection in vitro. When treated with serum or plasma, these assays detect the suppression of viral growth in cell culture. Neutralization tests are classified into three types:
  • Microneutralization tests use recombinant SARS-CoV-2 expressing reporter proteins or plaque-reduction neutralization tests (PRNTs). Up to five days may be required to complete these tests. Currently, there are no EUA-VNTs available.
  • A pseudovirus neutralization test (pVNT) utilizes recombinant pseudoviruses that contain the S protein of SARS-CoV-2 (such as the vesicular stomatitis virus [VSV] or lentivirus). BSL-2 laboratories can perform these reporter-based tests, depending on the virus strain. EUA pVNTs are not available at the moment.

An FDA EUA has authorized one competitive neutralization test (cVNT). These are binding antibody tests intended to identify possibly neutralizing antibodies, which typically inhibit the RBD from interacting with the ACE-2 receptor. In an ELISA format, the test replicates the interaction of the RBD with ACE-2 and the capacity of RBD-specific antibodies to disrupt the contact indicated by a drop in signal based on the reporter-fused RBD. Because these tests do not need a live virus, they may be performed in BSL-2 facilities.