['ABO glycosyltransferases catalyze antigen modifications on various glycans and glycoproteins and determine the ABO blood types. Blood type A has been associated with increased risk of vascular diseases and differential circulating levels of proteins related to inflammation and endothelial function. The objective of this study was to determine the association of ABO blood types with ARDS risk in patients with major trauma and severe sepsis.', 'We conducted prospective cohort studies in two populations at an urban tertiary referral, level I trauma center. Critically ill patients (n 5 732) presenting after major trauma were followed for 5 days for ARDS development. Additionally, 976 medical patients with severe sepsis were followed for 5 days for ARDS. Multivariable logistic regression was used to adjust for confounders.', 'ARDS developed in 197 of the 732 trauma patients (27%). Blood type A was associated with increased ARDS risk among whites (37% vs 24%; adjusted OR, 1.88; 95% CI, 1.14-3.12; P 5 .014), but not blacks (adjusted OR, 0.61; 95% CI, 0.33-1.13; P=.114). ARDS developed in 222 of the 976 patients with severe sepsis (23%). Blood type A was also associated with an increased ARDS risk among whites (31% vs 21%; adjusted OR, 1.67; 95% CI, 1.08-2.59; P=.021) but, again, not among blacks (adjusted OR, 1.17; 95% CI, 0.59-2.33; P=.652).'] Is aBO blood type A associated with increased risk of ARDS in whites following both major trauma and severe sepsis?