The second example of anti-Er(b) in a woman during her third pregnancy.

The Er blood group collection (ISBT symbol ER, ISBT number 208) was established as a blood group in 19901. It consists of two antigens: Era, first reported in 1982 and named after the first proband who produced the antibody, and the antithetical antigen Erb, first reported in 19882. Their respective occurrence in all populations is 100% (three Er(a−) European probands) and less than 0.01%.