Blood type A was associated with a greater risk of severe SARS-CoV-2 in one recent study and a higher risk of contracting the disease in another. "The two studies are complementary," Dr. James Szymanski of Montefiore Medical Center and Albert Einstein College of Medicine in New York City, coauthor of one of the reports, told Reuters Health by email. "Our study adds support that blood group A may confer a higher risk, whereas the other study gives one possibility as to the 'how' part. That study provides evidence that the SARS-CoV-2 receptor binding domain (RBD) directly interacts with respiratory cells through the blood group A antigen." "ABO blood type is a nonmodifiable risk factor, and current studies show the strength of the association as being limited," he noted. "Future studies need to prospectively confirm the association of ABO blood group with SARS-CoV-2 and further characterize the specific biological mechanisms that underlie it." As reported in Transfusion, Dr. Szymanski and colleagues analyzed electronic health record data on close to 5,000 patients (mean age, 62; about 48% men) hospitalized or with an emergency department visit who received a positive nucleic acid test result for SARS-CoV-2 from March 10, 2020-June 8, 2020. The all-cause mortality rate was 23%. To estimate overall risk by ABO type and account for the competing risks of in-hospital mortality and discharge, the team calculated the cumulative incidence function for each event. Cause-specific hazard ratios for in-hospital mortality and discharge were analyzed using multivariable Cox proportional hazards models to evaluate the effect of blood type after controlling for age, sex, body mass index, initial estimated glomerular filtration rate, and initial partial pressure of oxygen, as well as covariates. Type A blood was associated with the increased cause-specific hazard of death among COVID-19 patients compared to type O (HR, 1.17) and type B (HR, 1.32). Separately, Dr. Sean Stowell of Brigham and Women's Hospital in Boston and colleagues conducted a series of laboratory experiments to investigate the mechanism by which blood group antigens - particularly those of blood group A -might influence the risk for SARS-CoV-2 infection. As reported in Blood Advances, the team studied the SARS-CoV-2 RBD protein, the part of the virus that attaches to the host cells. They assessed synthetic blood group antigens on respiratory and red blood cells found in blood groups A, B, and O and analyzed how the SARS-CoV-2 RBD interacted with each blood type. They found that the RBD had a strong preference for binding to blood group A (but not to other blood types) on respiratory cells only, not red blood cells. The team also tested whether the RBD of SARS-CoV, the virus that causes severe acute respiratory syndrome (SARS), had a similar preference, and indeed it did. Like Dr. Szymanski, Dr. Stowell told Reuters Health, "whether blood group status truly influences the risk of SARS-CoV-2 infection or outcomes remains to be determined." "There is no indication that patients should be managed differently because of their blood type," he said by email. "As our understanding regarding the possible influence of blood group antigens on SARS-CoV-2 infection grows, it may be possible in the future to leverage this information to develop strategies to reduce infection risk. However, many studies need to be done before it is clear whether such strategies may even be possible. SOURCES: https://bit.ly/3vrZbDY Transfusion, online March 5, 2021, and https://bit.ly/3cuhrUI Blood Advances, online March 3, 2021. —Marilynn Larkin Source
