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Does Your Blood Type Predict COVID-19 Severity?

  • Authors: News Author: Marcia Frellick; CME Author: Charles P. Vega, MD
  • CME / ABIM MOC / CE Released: 8/20/2020
  • Valid for credit through: 8/20/2021
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Target Audience and Goal Statement

This article is intended for primary care physicians, infectious disease specialists, nurses, pharmacists, and other clinicians who care for patients at risk for infection with coronavirus disease 2019 (COVID-19).

The goal of this activity is to provide medical news to primary care clinicians and other healthcare professionals in order to enhance patient care.

Upon completion of this activity, participants will be able to:

  • Assess results from a previous study evaluating the risk for COVID-19 according to blood type
  • Evaluate whether blood type might affect the severity of COVID-19
  • Outline implications for the healthcare team


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News Author

  • Marcia Frellick

    Freelance writer, Medscape


    Disclosure: Marcia Frellick has disclosed no relevant financial relationships.

CME Author

  • Charles P. Vega, MD

    Health Sciences Clinical Professor of Family Medicine
    University of California, Irvine School of Medicine
    Irvine, California


    Disclosure: Charles P. Vega, MD, has disclosed the following relevant financial relationships:
    Served as an advisor or consultant for: Johnson & Johnson Pharmaceutical Research & Development, L.L.C.; Genentech; GlaxoSmithKline
    Served as a speaker or a member of a speakers bureau for: Shire

Editor/CME Reviewer

  • Esther Nyarko, PharmD

    Associate Director, Accreditation and Compliance, Medscape, LLC


    Disclosure: Esther Nyarko, PharmD, has disclosed no relevant financial relationships.

Nurse Planner

  • Amy Bernard, MS, BSN, RN-BC, CHCP

    Director, Accreditation and Compliance, Medscape, LLC


    Disclosure: Amy Bernard, MS, BSN, RN-BC, CHCP, has disclosed no relevant financial relationships.

Medscape, LLC staff have disclosed that they have no relevant financial relationships.

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Does Your Blood Type Predict COVID-19 Severity?

Authors: News Author: Marcia Frellick; CME Author: Charles P. Vega, MDFaculty and Disclosures

CME / ABIM MOC / CE Released: 8/20/2020

Valid for credit through: 8/20/2021


Note: This is the fifty-fourth of a series of clinical briefs on the coronavirus outbreak. The information on this subject is continually evolving. The content within this activity serves as a historical reference to the information that was available at the time of this publication. We continue to add to the collection of activities on this subject as new information becomes available.

Clinical Context

The research into COVID-19 continues at a blistering pace, and one issue that has captured the attention of the popular media is the potential interaction between blood type and the risk for COVID-19. There is precedent for blood type playing a role in infection. A study by Zhao and colleagues, which is currently in preprint[1] and has been the source of buzz regarding blood type and COVID-19, asserts that blood type affects the susceptibility to hepatitis B and Norwalk virus. Importantly, blood type was previously associated with susceptibility to the severe acute respiratory syndrome coronavirus.

A multifacility study has found no correlation between blood type and inflammatory markers but did find people with type O had a significantly lower chance of testing positive. In their study, Zhao and colleagues compared blood type among 2173 patients with COVID-19 and healthy control participants in China. They found that blood group A was associated with an odds ratio (OR) of 1.28 (95% CI: 1.14, 1.44) for COVID-19. Conversely, blood type O carried an OR of 0.68 (95% CI: 0.6, 0.77) compared with other blood types.

The current study by Latz and colleagues assessed whether blood type truly is a risk factor for COVID-19 and examined blood type as a potential prognostic factor among individuals with infection.

Study Synopsis and Perspective

Blood type is not a predictor of COVID-19 severity (death or intubation) or need for hospitalization, but it may be linked to testing positive for the disease, a new study has found.

Co-first authors Christopher A. Latz, MD, MPH, and Charles DeCarlo, MD, from the division of vascular and endovascular surgery at Massachusetts General Hospital (MGH) in Boston, Massachusetts, and colleagues, published their findings online July 12 in the Annals of Hematology.[2]

The observational study analyzed data from 1289 symptomatic adults with COVID-19 and documented blood type.

Patient information came from the Research Patient Data Registry, a large repository spanning 5 Boston-area hospitals, including MGH and Brigham and Women's Hospital. Patients underwent treatment from March 6 to April 16. Senior author Anahita Dua, MBChB, a vascular surgeon at MGH, told Medscape Medical News the study should put to rest one question surrounding COVID-19.

"Blood type does not relate to severity of disease in COVID," she said; however, other links between blood type and COVID-19 deserve further study.

A study by Ellinghaus and colleagues published in the New England Journal of Medicine[3] found a link between genetic markers and COVID-19.

In that study, the researchers identified a particular gene cluster among patients with COVID-19 and respiratory failure "and confirmed a potential involvement of the ABO blood-group system," according to Dua.

That may be an area ripe for more research, she continued.

"It's not unheard of that a genetic difference in people would result in a different outcome with COVID," Dua explained.

Type O Phenomenon

Dua said one interesting finding in the current research was that symptomatic patients with COVID-19 and type O blood appeared to test positive at a significantly lower rate than patients who had types B or AB or a positive rhesus (Rh) factor.

Table. Odds of a Positive COVID-19 Test by Blood Type

Blood Type aOR (95% CI
A 1 (0.88, 1.13)
B 1.28 (1.08, 1.52)
AB 1.37 (1.02, 1.83)
O 0.84 (0.75, 0.95)
Rh-positive 1.22 (1, 1.5)

Latz C, et al.[2]

A previous study in a preprint, which was not peer reviewed, concluded that among hospitalized patients in China, type A blood was associated with a higher risk of developing COVID-19 compared with non-A blood groups. It also showed that type O was linked with a lower risk for infection compared with non-O blood groups.

Latz and colleagues found no link with key clinical outcomes:

  • Hospital admission (P = .2)
  • Intensive care unit admission (P = .94)
  • Intubation (P = .93)
  • Required prone positioning while intubated (P = .58)
  • Required extracorporeal membrane oxygenation (P = .09)
  • Death (P = .49)

There was also no link to increased inflammation depending on blood type, with key markers including white blood cell count and C-reactive protein.

It would have been very interesting if patients with a certain blood type were not reacting with inflammatory signals when patients of another blood type were, Dua said, but the researchers found instead the same kind of inflammatory response.

Roy Silverstein, MD, professor and chair of medicine at the Medical College of Wisconsin, division of hematology and oncology, in Milwaukee, Wisconsin, told Medscape Medical News that none of these association studies should be considered conclusive, but the study by Latz and colleagues seems to be the most robust of the COVID-19 blood type studies.

"These kind of studies can never provide certainty," he said. "There are always potential biases."

He noted many blood type studies have used regular blood donors as a control, but that group has historically had an overrepresentation of type O because those universal donors are the ones blood banks most often solicit.

There is biological plausibility of a link between disease properties and blood type (eg, malaria), and Silverstein said he would not rule out that blood type could play some role in understanding COVID-19. He encouraged further study.

"It might point to areas for biologists to do interesting research," he said but he added he would never tell someone with type O blood to be less cautious about wearing a mask, washing hands, or social distancing.

"We all need to be extra cautious," he said.

Study Highlights

  • The study retrospectively reviewed cases of COVID-19 among adults at age ≥ 18 years who were tested at 1 of 5 major hospitals in Massachusetts. The study period was from March 6 to April 16.
  • Researchers assessed the study cohort for a broad range of chronic comorbid illnesses, as well as medication use. They also recorded laboratory values from admitted patients.
  • The main study outcome was the relationship between blood type and the composite outcome of intubation or death. The study analysis was adjusted to account for demographic and disease data.
  • 7648 symptomatic adults received COVID-19 testing during the study period, and 1289 tests were both positive and also included information on blood type. The mean age of study participants was 56.6 ±18.68 years, and the majority (~ 67%) were female. Black adults comprised > 20% of the study population, and Hispanic adults represented > 10% of the cohort.
  • 37.5% of patients were admitted to the hospital, and 9.5% entered the intensive care unit; 8.4% of patients were intubated; and 6.9% died.
  • The distribution of blood types among patients with a positive test for COVID-19 were as follows:
    • A -- 34.1%
    • B -- 15.6%
    • AB -- 4.7%
    • O -- 45.5%
  • Blood type was not significantly associated with inflammatory markers, such as white blood cell count, lactate dehydrogenase, C-reactive protein, or erythrocyte sedimentation rate.
  • Blood type also did not affect the risk for any clinical outcomes, including hospitalization, intubation, or death.
  • In multivariate analysis, blood types B (OR = 1.28 [95% CI: 1.08, 1.52]) and AB (OR = 1.37 [95% CI: 1.02, 1.83]) were associated with a higher risk of testing positive for COVID-19. The respective OR for blood type A was 1 (95% CI: 0.88, 1.13), and blood type O appeared protective against COVID-19 (OR= 0.84 [95% CI: 0.75, 0.95]). In addition, Rh-positive blood was associated with an OR of 1.22 (95% CI: 1, 1.5) for COVID-19.

Clinical Implications

  • In a yet-to-be-published study by Zhao and colleagues, type A blood was associated with a higher risk for COVID-19 whereas type O blood was protective against infection.
  • In the current study by Latz and colleagues, blood type was not associated with the severity of COVID-19. Blood types B and AB were associated with a higher risk for infection, and blood type O again appeared protective against infection.
  • Implications for the Healthcare Team: Controversy surrounds the role of blood type in susceptibility to COVID-19, but the current study suggests that blood type does not correlate with the severity of infection. Clinicians should continue to consider evidence based treatment options for patient infected with COVID-19.


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