Influence of ABO blood type on symptomatology among outpatients: study and replication

Two independent samples of psychiatric outpatients (n = 52 and 60) with blood type A or O completed the Brief Symptom Inventory, an abbreviated version of the SCL-90. In both samples patients with blood type A scored significantly higher than those with type O on the 'Obsessive-Compulsive' and 'Psychoticism' factors. These findings are not attributable to differences in age, sex or diagnosis, and are consistent with several previous studies. The influence of blood type on symptom expression may be mediated by cell membrane characteristics.