ABO blood group and rhesus factor association with inpatient COVID-19 mortality and severity: a two-year retrospective review.

Background: Early reports have indicated a relationship between ABO and rhesus blood group types and infection with SARS-CoV-2. We aim to examine blood group type associations with COVID-19 mortality and disease severity.

Methods: This is a retrospective chart review of patients ages 18 years or older admitted to the hospital with COVID-19 between January 2020 and December 2021. The primary outcome was COVID-19 mortality with respect to ABO blood group type. The secondary outcomes were 1. Severity of COVID-19 with respect to ABO blood group type, and 2. Rhesus factor association with COVID-19 mortality and disease severity. Disease severity was defined by degree of supplemental oxygen requirements (ambient air, low-flow, high-flow, non-invasive mechanical ventilation, and invasive mechanical ventilation).

Results: The blood type was collected on 596 patients with more than half (54%, N=322) being O+. The ABO blood type alone was not statistically associated with mortality (P=0.405), while the RH blood type was statistically associated with mortality (P<0.001). There was statistically significant association between combined ABO and RH blood type and mortality (P=0.014). Out of the mortality group, the O+ group had the highest mortality (52.3%), followed by A+ (22.8%). The combined ABO and RH blood type was statistically significantly associated with degree of supplemental oxygen requirements (P=0.005). The Kaplan-Meier curve demonstrated that Rh- patients had increased mortality.

Conclusion: ABO blood type is not associated with COVID-19 severity and mortality. Rhesus factor status is associated with COVID-19 severity and mortality. Rhesus negative patients were associated with increased mortality risk.