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Blood type and outcomes in patients with COVID-19

Our take —

Contrary to previous studies, blood type A was not associated with testing positive for COVID-19. Blood types AB and B were associated with increased odds of testing positive for COVID-19, while blood type O appeared slightly protective. None of the blood types were associated with intubation or death. The results may not be widely generalizable, as only patients with recorded blood type were included, and residual confounding may exist.

Study design

Retrospective Cohort

Study population and setting

The goal of this study was to examine whether there is a relationship between ABO blood typing and testing positive for COVID-19 or severity of COVID-19 disease. The population included symptomatic adults at five major hospitals in Massachusetts (Partner’s Healthcare System’s Research Patient Data Registry) who were tested for COVID-19 and had blood type recorded. Disease comorbidities were extracted from the medical record based on ICD-9/10 codes and medication history was reviewed over the previous year. The main outcome of interest was COVID-19 severity, defined as intubation or death.

Summary of Main Findings

Among the 7648 symptomatic patients who received a COVID-19 test during the study period, 1289 (16.9%) tested positive for COVID-19, and of those, 162 (12.6%) were intubated or died. In multivariable analyses, adjusting for sex, primary language, age, and rhesus factor with all other blood types as the reference, blood types AB (OR: 1.28, 95% CI: 1.108-1.52) and B (OR 1.37, 95% CI: 1.02-1.83) had higher odds of positive tests, and blood type O (OR=0.84, 95% CI: 0.75-0.95) had a lower odds of testing positive; Rhesus factor was also associated with testing positive (OR=1.22, 95% CI: 1.00-1.50). None of the blood types or Rhesus factor were associated with COVID-19 disease severity (intubation or death) in multivariable analysis.

Study Strengths

This was a relatively large, multi-site study. No data were missing for demographics, comorbidities, or medications.


Only participants with recorded blood type were included in the study; how many patients without blood type information were excluded is not reported. Although this missingness is likely random (unrelated to blood type) and would not largely impact the observed association between blood type and COVID-19 test results or disease severity, it may limit the generalizability of the findings, as patients with recorded blood type may be different than patients without recorded blood time in regards to demographics or medical history. The duration of patient follow-up is not reported, and it is possible that some included participants went on to develop severe COVID-19.

Value added

This study adds to a growing body of literature about the relationship between ABO blood type and COVID-19 testing resultings, and is one of the first to examine the relationship between ABO blood type and disease severity.

This review was posted on: 3 August 2020