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Disclosures: Barington and Sekhon report no relevant financial disclosures. Please see the study for all other authors’ relevant financial disclosures.
October 14, 2020
3 min read

Blood type may be linked to risk for COVID-19 infection, likelihood of severe outcomes

Disclosures: Barington and Sekhon report no relevant financial disclosures. Please see the study for all other authors’ relevant financial disclosures.
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People with blood type O may be less likely to develop COVID-19 infection, and they may have a lower risk for severe outcomes if they contract the virus, according to results of two studies published in Blood Advances.

Previous studies have shown several factors — including age, sex and comorbidities, such as cardiovascular disease — are associated with COVID-19 infection. However, severe cases are not limited to these risk groups.

Blood Donation
Source: Adobe Stock.

Other studies have suggested a potential role of ABO blood groups in risk for infection.

“ABO blood groups are increasingly recognized to influence susceptibility to certain viruses, including SARS-CoV-1 and norovirus,” Torben Barington, MD, professor of medicine at Odense University Hospital and University of Southern Denmark, and colleagues wrote. “A, B and AB individuals are also at increased risk for thrombosis and cardiovascular diseases, which are important comorbidities among hospitalized COVID-19 patients, possibly mediated by glycosylation of proteins involved in hemostasis.”

Infection risk

In a retrospective cohort study, Barington and colleagues analyzed data of over 840,000 individuals in Denmark who underwent testing by polymerase chain reaction for SARS-CoV-2 between Feb. 27 and July 30. Most of those tested (56%) had available ABO and RhD blood group information.

Researchers used ABO and RhD data of 2,204,742 individuals not tested for SARS-CoV-2 as a reference. This corresponded to approximately 38% of the entire Danish population.

ABO and RhD blood groups and test results for SARS-CoV-2 served as the primary outcome. Hospitalization and death due to COVID-19 served as secondary outcomes.

Of the 473,654 tested individuals who had a known blood group, 7,422 were positive for SARS-CoV-2 and 466,232 were negative.

The positive and negative groups had similar proportions of men (32.9% vs. 32%) and similar median ages (52 years vs. 50 years).

Results showed a small but statistically significant difference in blood group distribution between those with SARS-CoV-2 and those in the reference population (P < .001).

Among patients with SARS-CoV-2, considerably fewer (38.4%) had blood type O than other tested blood types (P < .001). When excluding blood type O, researchers observed no significant differences among patients with blood types A, B and AB. They also observed no difference in the RhD group between positive cases and the reference population.

The investigators reported RRs for contracting SARS-CoV-2 of 0.87 (95% CI, 0.83-0.91) for blood type O, 1.09 (95% CI, 1.04-1.14) for blood type A, 1.06 (95% CI, 0.99-1.14) for blood type B and 1.15 (95% CI, 1.03-1.27) for blood type AB.

“It is very important to consider the proper control group because blood type prevalence may vary considerably in different ethnic groups and different countries,” Barington said in a press release. “We have the advantage of a strong control group because Denmark is a small, ethnically homogeneous country with a public health system and a central registry for lab data. So, our control is population-based, giving our findings a strong foundation.”

Mechanical ventilation

Previous studies in vitro have shown the anti-A antibody — found in individuals with blood type O or B — antagonizes the interaction between SARS-CoV-1 and the receptor for angiotensin-converting enzyme 2 (ACE2), which host target cells express.

Because SARS-CoV-2 also binds to ACE2, these blood groups also may be determinants of susceptibility to SARS-CoV-2 infection, according to researchers.

Mypinder S. Sekhon, MD, clinical assistant professor in the division of critical care medicine and department of medicine at University of British Columbia, sought to identify potential associations of blood groups with severity of COVID-19 infection among 95 critically ill patients admitted to the ICU between March 1 and April 28 at six hospitals in the Vancouver area. Fifty-seven patients had blood type O or B. The other 38 patients had blood type A or AB.

The proportion of patients requiring mechanical ventilation served as the primary outcome. The probability of requiring mechanical ventilation during a hospital stay served as a secondary outcome.

Results showed a greater proportion of patients with blood type A or AB required mechanical ventilation compared with blood type O or B (84% vs. 61%; P = .02). After adjusting for sex, age, comorbidity status and treating death as a competing risk, researchers found patients with blood type A or AB had a greater probability of requiring mechanical ventilation (adjusted subdistribution HR [sHR] = 1.76; 95% CI, 1.17-2.65) or continuous renal replacement therapy (adjusted sHR = 3.75; 95% CI, 1.28-10.9). They also had a longer median ICU stay than patients with blood type O or B (13.5 days vs. 9 days; P = .03).

“The unique part of our study is our focus on the severity effect of blood type on COVID-19,” Sekhon said in the press release. “Of particular importance as we continue to traverse the pandemic, we now have a wide range of survivors who are exiting the acute part of COVID-19, but we need to explore mechanisms by which to risk stratify those with longer-term effects.”