ERCIYES MEDICAL JOURNAL, cilt.43, sa.6, ss.624-625, 2021 (ESCI)
Dear Editor,
We have read with great interest the publication entitled “The Relationship between Blood Groups and patients with COVID-19 (1).” In the study, the author points out that the frequencies of blood groups in patients
with COVID-19 and recommends that “people with blood type A behave more sensitively in terms of following the protection measures.” In this study, there is not a control group that represents the population. The
blood group variable is compared within the patient group. The author cited Cekdemir’s study (2) for reference, but no statistical comparison was made between the two studies. Moreover, we see that the distribution
of blood groups are varied within the regions in Turkey (2). Without a proper control group, evaluating the
blood groups cannot give us a view or risk ratio for the entire population. We know there are some studies
from different countries regarding the ABO blood groups and COVID-19. A recent meta-analysis suggests
that blood type A may be more susceptible to infect COVID-19, while blood type O may be less susceptible
to infect COVID-19 (3). A recent study from Turkey (4) that has an own reference group which is compared
statistically also shows similar results. On the other hand, Dzik et al. (5) pointed that selecting a proper control
group is crucial for these studies. Simple blood bank donors may not be a suitable reference group because
blood donors are known to be selected in favor of blood group O persons who preferred as donors. ABO
blood group also varies by ethnicity, and this may influence the observed ABO distribution when comparing
patients versus uninfected group. Without a proper reference population comparison within this framework,
this study cannot directly show a risk towards a specific blood group in COVID-19. Additionally, the author
concluded that “a statistically significant difference was found concerning the symptom of cough according
to the blood groups of the patients.” However, in the last paragraph, the author concluded that “there was
no difference between the symptom states according to blood groups.” If there were a difference, it would be
better to show in which groups.