Is ABO blood group truly a risk factor for thrombosis and adverse outcomes?

Table 1 The incidence of ABO phenotypes in populations from different racial backgrounds

Race	Blood group phenotype	Blood group genotypes
	O1 (O2 rare)	A1	A2	B	A1B	A2B
Caucasian	44%	33%	10%	9%	3%	1%
Asian	43%	27%	Rare	25%	5%	Rare
African	49%	19%	8%	20%	3%	1%

Illustrations: Sub-group A2 expresses less A antigen on the red cell surface and has been referred to as “weak” A.