Intermountain Healthcare

No, your blood type doesn't affect risk of COVID-19 or severe illness, new Utah study finds

By Carter Williams, KSL.com | Posted - Apr. 15, 2021 at 2:35 p.m.


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SALT LAKE CITY — Your blood type does not factor in your risk for contracting COVID-19 or developing a severe case of it, researchers at Intermountain Healthcare and other institutions determined.

Their findings, published in the Journal of American Medical Association earlier this month, counters previous global studies and research that suggested blood type was one factor for why some people suffered symptoms of COVID-19 more than others.

"I think it's important because it's been, for us, really one of our primary objectives to identify patients who are at higher risk and to build risk scores," said Dr. Jeffrey Anderson, a cardiologist and researcher with the Intermountain Medical Center Heart Institute, and the study's lead researcher.

Hospitals use all sorts of possible risks to determine if someone should be hospitalized or not, or what other care they should receive. The results of the study indicate that ABO blood type is not a factor needed to evaluate risk.

Anderson explained that the study was prompted by the many unknowns within COVID-19. Medical professionals all over the world had little to no answers regarding why some people got sicker than others. If they could solve the puzzle, then they could help provide better treatment for patients.

The data pinpointed older people, as well as people with high obesity, diabetes, high blood pressure and pre-existing lung or heart conditions. But since COVID-19 ravaged China and Europe before the U.S., global researchers got a head start on potential other factors.

A study that emerged in China early last year piqued Anderson's interest. It suggested blood type played a role in contracting COVID-19. More specifically, it suggested that those with blood type A had a higher risk of contracting COVID-19 and blood type O had a lower risk of being infected.

Researchers in Italy and Spain then released a study that suggested that blood type didn't factor in contracting COVID-19 but did factor into the severity of a new case. In a somewhat similar result, the research suggested blood type A resulted in more severe cases and type O resulted in less severe. It's unclear how much medical professionals relied on these studies in how they handled COVID-19 treatment.

"We started getting interested in this and wondered whether we should look into this as well, especially as other reports came out that had variable results," Anderson said. "There was one from Denmark that, in contrast, said it was infectivity but not the severity of disease impacted, and then here out of the U.S. from New York and Boston … where there was no risk association."

So researchers from Intermountain Healthcare, the University of Utah School of Medicine, and Stanford University sought to confirm the findings of the earliest studies.

They examined the results of 107,796 people tested for COVID-19 in Utah, Idaho and Nevada between March 3, 2020, and Nov. 2, 2020. Anderson said the health care database provided a gold mine for researchers since it provided them with the patients' COVID-19 test results and their blood types. It also provided information regarding how severe a case got if someone ended up hospitalized.

Roughly 10.6% of the nearly 108,000 people involved in the study tested positive for COVID-19, according to the data. Broken down by blood type, researchers found that the percentage of people who tested positive for COVID-19 essentially mirrored the percentage who tested negative.

Blood type A, for instance, accounted for 39.6% of positive results but also 40.4% of negative results. Type B accounted for 9% of positive and 9.3% of negative. Type AB accounted for 3.2% positive and 3.3% negative, while type O accounted for 48.1% positive and 47.1% negative.

"There was no relationship between ABO type and the risk of being infected," Anderson said.

Similar patterns emerged in hospitalizations and intensive care unit cases. Of the 11,468 positive cases, 2,326 ended up hospitalized; and 706 of those hospitalized ended up in the ICU.

Again, blood type accounted for 38.6% of hospitalizations and 39.9% of nonhospitalized cases. It accounted for 36.4% of ICU stays and 39.5% of non-ICU hospitalization cases.

Type B accounted for 8.8% of hospitalizations and 9.1% of non-hospitalizations, as well as 8.6% of ICU cases and 8.9% of non-ICU cases. Type AB represented 3.4% of hospitalizations and 3.1% of cases that didn't need hospitalization; it accounted for 2.8% of ICU cases and 3.6% of cases where the ICU wasn't needed.

Finally, 49.2% of hospitalizations involved persons with type O blood compared to 47.9% of cases where no hospitalization was needed; it also accounted for 52.1% of all ICU cases in the data compared to 48% of no hospitalization.

The results were somewhat of a surprise for researchers, especially since studies over the years have found connections between type A blood and risk for heart attack, Anderson said.

"We had gone into this study thinking we would probably validate or verify the reports of a relationship but we found none," he said.

That's not to say the research didn't find other connections. The data confirmed theories that older individuals, men and those in minority communities were at higher risk for contracting COVID-19 or developing severe disease from it.


I think it's extremely important that we learn everything we can about this virus so we can best combat it.

–Dr. Jeffrey Anderson, a cardiologist and researcher with the Intermountain Medical Center Heart Institute


Anderson added that it's also possible that the findings are regional. There's a potential that other factors led other global regions to find different results.

"Blood type does vary in terms of its frequency among different populations and so forth," he said. "There may be different associations with blood type that explains some of the other results, differing results from other areas.

"In other words, blood types might be linked to some other characteristics that cause disease or puts people at risk," he continued. "This is called an association, and that's different than what we'd call a risk factor that's causal."

For researchers like Anderson, finding no correlation between blood type and risks from COVID-19 is one piece closer to solving the COVID-19 puzzle.

It adds to the growing list of items learned since SARS-CoV-2 and COVID-19 were first identified in late 2019. Since SARS-CoV-2 was a novel coronavirus, it meant medical experts began with the same knowledge as anyone else about how it spread and how it affects humans.

"I think it's extremely important that we learn everything we can about this virus so we can best combat it," Anderson said. "We're not through yet. It's wonderful to see the light at the end of the tunnel, to see our numbers coming down, but this is going to be with us still at some level for, I think, the next many months and perhaps years.

"The more we can learn about it the better off we are."

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