ABO blood group system, age, sex, risk factors and cardiac infarction.

In a retrospective study in 3100 patients of different ages the relationship between blood group and cardiac infarction was investigated in 450 patients. The patients were divided in two age groups: those who were 65 yr old and older and younger patients (age less than 65 yr). The predominance of blood group A in patients with cardiac infarction was highly significant in both age groups (P less than 0.005, two-tailed Chi-square test). Step-wise excluding all patients with at least one of the risk factors, hypertension, hyperuricemia, diabetes mellitus, smoking, and hyperlipemia similar results were found: the predominance of blood group A in the elderly patients with cardiac infarction was even higher than before excluding the risk factors (P less than 0.001). The predominance of blood group A was also demonstrated at a lower level in younger patients with cardiac infarction (P less than 0.05). Our investigation strongly suggests the existence of a genetic factor associated with blood group A and independent of the other risk factors which is also responsible for a greater incidence of cardiac infarction.