This is a hospital-based retrospective cohort study and the Immunohematologic characteristics of COVID-19 patients will be investigated systematically.

This is a hospital-based retrospective cohort study and the Immunohematologic characteristics of COVID-19 patients will be investigated systematically. In this study, we will seek to understand the association between SARS-CoV-2 infection and blood groups and explore the Anti-A and Anti-B effects in COVID-19 patients with graded severity. We will analyze the transfusion requirement and the clinical recurrences of COVID-19 patients. The discrepancy of blood group phenotypes in COVID-19 patients with graded severity will be also analyzed on the molecular level. This retrospective cohort study was conducted using electronic health recording data in Tongji Hospital. The clinical characteristics for all eligible patients will be retrieved. The records will be verified to avoid possible bias. Data collection was carried out independently by two investigators and reviewed by two different investigators.

Inclusion Criteria:

• The patients who were diagnosed with COVID-19 following the WHO interim guidelines (https://www.who.int/publications-detail/clinical-management-of-severe-acute-respiratory-infection-when-novelcoronavirus-(ncov)-infection-is-suspected. 2020.)

Exclusion Criteria:

• Male or female patients <18 years of age

The patients were diagnosed with COVID-19 following the WHO interim guidelines and admitted for treatment in Tongji hospital. The admission dates were January 01 2020 to April 01, 2021. Male or female patients <18 years of age were excluded.