The results of this study showed that the blood group distributions in severe, non-severe, and non-COVID-19 patients were A = B > O > AB, O > A > B > AB, and O > B > A > AB, respectively. The distribution of blood type O in the severe COVID-19 group was significantly different from that in the non-COVID-19 group. There was a negative correlation between blood type O and the risk of severe COVID-19 infection, but there were no significant differences between the distributions of other blood groups and severe COVID-19 infection risk. The number of female patients with blood type O with severe COVID-19 was significantly different from that in the non-COVID-19 group, and there were no significant differences in other blood groups. This study is different from ones conducted earlier[16, 17] as the gender and the blood type distribution make association with risk of severe COVID-19 patients.
The gene encoding the ABO blood group system is very stable and is located on the long arm of chromosome 9 at the band 9q34. It is closely associated with many diseases [10, 18, 19]. Glenda et al. [20] found the blood group antigen expression to be different across regions and populations because of natural selection and the effect of an external factor. Liao et al. [21] suggested that the A, B, and AB blood types might be susceptible to norovirus infection; however, blood type O appeared to be more susceptible to norovirus infection. Jing et al. [22] performed a meta-analysis to investigate whether the ABO blood groups were associated with hepatitis B virus (HBV) infection. They found a correlation between the ABO blood groups and the incidence of eight types of cancers [23].
In this study, the blood group results of COVID-19 patients were analysed retrospectively. The non-COVID-19 patients who all returned from Wuhan or had a history of contact with people who returned from Wuhan contact were significantly different between the 'Wuhan returners' and 'contact history with people from Wuhan' groups. This may be due to the variations in epidemic situations in different areas of Wuhan and the different frequency of personal protective activities, but the electronic medical records did not contain this information in detail. We found that patients with COVID-19 were generally older than non-COVID-19 patients, and there was a significant difference in the comorbidity of gastric disease between the COVID-19 and non-COVID-19 patients (12.3% vs. 3.7%, respectively; χ2 = 5.291, p = 0.021).
Blood group antigens can modify the innate immune response to infection [24]. Patients with blood type A had an increased risk of infection with SARS-CoV-2, whereas those with blood type O had a decreased risk, indicating that certain ABO blood groups were correlated with SARS-CoV-2 [18], and the distribution ratio of blood types A and O across various ages and genders was almost consistent with the trend in value found in other studies [25].
We divided the COVID-19 patients into type O and non-type-O blood groups and analysed the comorbidity data and laboratory indices in the two groups. The results indicated that there were no significant differences in the comorbidity data, and there is currently no literature showing that diabetes, hypertension, chronic pulmonary disease, gastric disease, kidney disease, or hepatitis increases the risk of infection of SARS-CoV-2. However, we found that ALT (alanine aminotransferase), LDH (Lactate dehydrogenase), and TBCD19 (Total CD19+B cell ratio) were lower in type O COVID-19 patients, while their MCV had a higher value. MCH values showed significant differences between the type O and non-type-O COVID-19 patient groups. ALT is mainly distributed in the liver, followed by the skeletal muscle, kidneys, heart muscle, and other tissues. It is one of the most sensitive indicators of liver damage. LDH is an enzyme found in the cytoplasm of nearly all cells in the human body and is used to detect cell necrosis and tissue destruction [26]. One study [22] indicated that the relationship between LDH and in-hospital mortality in patients with acute aortic dissection was non-linear. LDH was positively associated with in-hospital mortality when it was more than 557 U/L. Another study showed that idiopathic pulmonary arterial hypertension patients with high LDH levels had a low cumulative survival rate [27]. CD19 is a common surface marker of all B cells. B cells mainly mediate humoral immunity such as anti-infection, MCV, MCH, and mean corpuscular haemoglobin concentration (MCHC). They often declared the pathological changes of red blood cells from different sides, which had a value for the diagnosis of anaemia, which suggested that the damage to the liver and myocardium in COVID-19 patients with blood type O was less serious than that in patients with non-type O.