COVID-19 Serology Patient Surveillance

Houston Methodist Hospital System has implemented COVID-19 serology testing on all admitted patients. This is a Quality Improvement Project to determine the potential future clinical utility of COVID-19 Anti-Spike IgG Antibody Titers (levels) in managing COVID-19 patients and to assist understanding when booster vaccination may be warranted. The project is not research as confirmed by our Research Regulatory Office and the human subjects IRB. Specific patient consent is not required. The results of the test will be reported in Epic. Please note that serum antibodies are only one component of specific immunity. Antibody measurement does not assess T-cell immunity status or contribution, or memory immune response.

Our COVID-19 Anti-Spike IgG Antibody Titer Assay is a laboratory developed test that is specific for IgG directed against spike protein of SARS-CoV-2. It uses purified recombinant Spike protein as target antigen. Guidance from the FDA is that this test does not require an Emergency Use Authorization. However, notification of use and submission of the test validation data to the FDA is required. These were completed before the test was implemented. The test has been available for clinical use for many months.

The COVID-19 Anti-Spike IgG Antibody Titer Assay is a quantitative ELISA. The preferred specimen is serum collected in a SST tube. The test is most often reported the next day and is not available STAT.

• A negative result is reported as titer <1:50
• A positive result is titer of 1:50 or greater
• The highest titer reported routinely is >1:1350

The purpose of this COVID-19 Serology Patient Surveillance is to generate data to help develop best clinical practices for management of COVID-19. The current interpretative information is:

• The COVID-19 Anti-Spike IgG Antibody Titer test is not used to diagnose infection with SARS-CoV-2.
• Positive results in this test can occur in patients following either vaccination (all 3 of the currently available vaccines in the US are based on SARS-CoV-2 Spike protein), previous infection with SARS-CoV-2, treatment with commercial monoclonal antibodies directed against Spike protein, or treatment with convalescent plasma containing antibodies directed against Spike protein.
• Although the antibody titer/level that equates to immunity from COVID-19 infection is not known, conventional wisdom is that some anti-Spike antibodies are good, and a higher titer/level of anti-Spike antibodies is better.
• The assay has been compared to two in vitro SARS-CoV-2 live-virus neutralization assays, and data have been published in peer-reviewed journals (e.g., American Journal of Pathology, Journal of Clinical Investigation, Communications Biology). Serum with an anti-Spike antibody titer of 1:450 and above showed significant inhibition of host-cell infection by live SARS-CoV-2 in these in vitro assays.
• The Houston Methodist COVID-19 Scientific Committee is considering a target of 1:450 or greater as a level that may not require a vaccine booster soon.

Please direct any questions to David W. Bernard, MD, PhD.