Prognostic Value of SARS-CoV-2 Anti-RBD IgG Antibody Quantitation on Clinical Outcomes in Hospitalized COVID-19 Patients

Background: Antibody levels against SARS-CoV-2 can be used as an indicator of recent or past vaccination or infection. However, the prognostic value of antibodies targeting the receptor binding protein (anti-RBD) in hospitalized patients is not widely reported. Purpose: Determine prognostic impact of SARS-CoV-2 antibody quantification at the time of admission on clinical outcomes in hospitalized COVID-19 patients. Methods: We conducted a pilot observational study on patients hospitalized with SARS-CoV-2 infection to determine the prognostic impact of antibody quantitation within the first two days of admission. Anti-nucleocapsid IgG (anti-N) and Anti-RBD levels were measured. Anti-RBD level of 500 AU/mL was used as a cutoff to stratify patients. Spearman's rank Coefficient (r(s)) was used to demonstrate association. Results: Of the 26 patients included, those who were vaccinated more frequently tested positive for Anti-RBD (100% vs 46.2%, P = 0.005) with higher median titer level (623 vs 0, P = 0.011) compared to unvaccinated patients. Anti-N positivity was more frequently seen in unvaccinated patients (53.9% vs 7.7%, P = 0.03). Anti-RBD levels > 500 were associated with lower overall hospital length of stay (LOS)(5 vs 10 days, P = 0.046). The analysis employing a Spearman Rank coefficient demonstrated a strong negative correlation between anti-S titer and LOS (r(s)= -.515, p = 0.007) and a moderate negative correlation with oxygen needs (r(s) =-.401, p = 0.042). Conclusion: Anti-RBD IgG levels were associated with lower LOS and oxygen needs during hospitalization. Further studies are needed to determine if levels on admission can be used as a prognostic indicator.