Be positive! That’s my motto and also my blood type. But is this a hidden risk factor for coronavirus disease 2019 (COVID-19)? Recent reports have added to the hypothesis that blood type is linked to COVID-19. Should we be concerned about these new findings?

COVID-19 and Blood Type: Quick Review

First, let’s review the blood type basics. Your blood type is determined by the presence or absence of specific antigens (A and B) on the surface of the red blood cells and antibodies (A and B) in the plasma (American Red Cross, 2020). In addition to the A and B antigens and antibodies, there is a protein called the Rh factor, which can be present (+) or absent (-). Combining these components results in eight common blood types: A+, A-, B+, B-, O+, O-, AB+, AB-. For nurses, knowing your patient’s blood type is critical when administering blood products to prevent lethal transfusion reactions.
 

ABO Blood Groups
Group	Red Blood Cells	Plasma	Can donate to:	% US Population*
A+	A Antigen	B Antibody	A+, AB+	36%
A-			A+, A-, AB+, AB-	6%
B+	B Antigen	A Antibody	B+, AB+	9%
B-			A+, A-, AB+, AB-	2%
AB+	AB Antigens	None	AB+ (Universal recipient)	3%
AB-			AB+, AB- (Universal Plasma Donor)	0.6%
O+	None	A and B Antibodies	O+, A+, B+, AB+	37%
O-			Universal Donor	7%

*Reference: WebMd, 2020

Is Blood Type Linked to COVID-19?

Research conducted on the first severe acute respiratory syndrome coronavirus-1 (SARS-CoV-1) found the anti-A antibody in people with blood group O or B may block the interaction between the virus and the receptor for angiotensin converting enzyme 2 (ACE2) found in cells, a mechanism for virus transmission (Guillon et al., 2008). SARS-CoV-2 also binds to ACE2 and therefore, may also be affected by the anti-A antibody. Additional studies found patients with blood group O have reduced levels of factor VIII and von Wilebrand factor, potential determinants which may provide a protective effect against vascular abnormalities in the pulmonary system (Hoiland et al., 2020).
 
A study conducted in the earlier days of the SARS-CoV-2 pandemic by Zhao et al. (2020) evaluated 2,173 patients and found the ABO blood group to be a biomarker for COVID-19 susceptibility. Their research showed blood group A individuals had a higher risk for COVID-19 and blood group O was associated with a lower risk for the infection compared with non-O blood groups. This study had several limitations in that the sample size was small and the control population lacked information on subject age, sex and chronic medical conditions, preventing a proper analysis to adjust for these factors.
 
Two recent studies on Covid and blood type were published this month (October 2020) in the journal Blood Advances supporting the theory that individuals with blood type O are at a lower risk for contracting COVID-19 and severe coronavirus illness.
 
The first investigation led by Hoiland et al. (2020) evaluated whether ABO blood groups are associated with different severities of COVID-19. This was a multicenter retrospective analysis and prospective observational sub-study of critical care patients (n = 95). Their investigation found a higher proportion of COVID-19 patients with blood group A or AB required mechanical ventilation and continuous renal replacement therapy (CRRT) and had a longer intensive care unit (ICU) stay (13.5 days) compared with patients with blood group O or B. Biomarkers of renal (serum creatinine) and hepatic dysfunction (AST, ALT) were higher in blood Group A or AB patients. These results indicate severe lung impairment as well as worsening kidney and liver disease. Inflammatory cytokines did not differ between patients with blood group A or AB versus O or B and overall hospital length of stay did not differ between groups. This study has several limitations. First, as a retrospective analysis of observational data, the investigators could not prove causality. Second, the sample size was small, lacking statistical power. In addition, the titer of anti-A antibodies can affect COVID-19 severity and these levels were not analyzed, but instead inferred from blood group data.
 
The second study conducted in Denmark by Barnkob et al. (2020) was a large retrospective cohort analysis designed to determine the influence of common blood types on virus susceptibility. The analysis compared over 473,000 people with COVID-19 to more than 2.2 million people in the general population. Of the COVID-19 positive individuals, considerably fewer blood type O individuals were found compared to a higher percentage of A, B, and AB individuals. There was no difference between ABO blood groups and clinical severity of COVID-19 for non-hospitalized patients versus hospitalized patients or for deceased patients versus living patients. The investigators concluded that blood group O is associated with reduced susceptibility to SARS-CoV-2 infection compared to type A, B and AB. However, ABO blood types did not correlate with rates of hospitalization or death following infection.
 

How do these studies on COVID and blood type impact clinical practice?

While preliminary studies point to a strong association, we don’t know yet how this will affect clinical practice. Further research is required to determine if ABO blood typing should be utilized in the management of SARS-CoV-2 infection and whether COVID-19 patients with non-O blood types require more aggressive treatment. Until more data is collected, clinicians should continue to follow current protocols in the care of COVID-19 patients. In addition, the public must remain vigilant in their responsibility to wear masks, maintain physical distancing, and continue strict hand hygiene.
 

COVID and Blood Type References

American Red Cross (2020). Facts About Blood and Blood Types. Retrieved from https://www.redcrossblood.org/donate-blood/blood-types.html
 
Barnkob, M.B., Pottegard, A., Stovring, H., Haunstrup, T.M., Homburg, K., Larsen, R., Hansen, M.B., Tiltlestad, K., Aagaard, B. Moller, B.K. & Barinton, T. (2020). Reduced prevalence of SARS-CoV-2 infection in ABO blood group O. Blood Advances. 4(20), 4990 – 4993. DOI: 10.1182/bloodadvances.2020002657 

Guillon, P., Clement, M., Sebille, V., Rivain, J., Chou, C., Ruvoen-Clouet, N., Le Pendu, J. (2008). Inhibition of the interaction between the SARS-CoV spike protection and its cellular receptor by anti-histo-blood group antibodies. Glycobiology. 18(12), 1085-1093. Doi: 10.1093/glycob/
 
Hoiland, R.L., Fergusson, N.A., Mitra, A.R., Griesdale, D.E.G., Devine, D.V., Stukas, S., Cooper, J., Thiara, S., Foster, D., Chen, L.Y.C., Lee, A.Y.Y., Conway, E.M., Wellington, C.L., Sekhon, M.S. (2020). The association of ABO blood group with indices of disease severity and multiorgan dysfunction in COVID-19. Blood Advances. 4(20), 4981 – 4989. DOI: 10.1182/bloodadvances.2020002623 
 
WebMD. (2020). Blood types: What to know - the different blood types. Retrieved from https://www.webmd.com/a-to-z-guides/blood-types-what-to-know#1
 
Zhao, J., Yang, Y., Huang, H., Li, D., Gu, G., Lu, X., Zhang, Z., Liu, T., Liu, Y., He, Y., Sun, B., Wei, M., Yang, G., Wang, X., Zhang, L., Zhou, X., Xing, M., and Wang, P.G. (2020). Relationship between the ABO Blood Group and the COVID-19 Susceptibility. Clinical Infectious Disease. 2020 Aug 4. DOI: https://doi.org/10.1101/2020.03.11.20031096

 
  

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