GSTM1 and thalassemia: Hbs Hope, Tak, Cook, C, Lepore, and Q-Thailand were found to be associated with high proportions of the error.<h4>Conclusions</h4>Hb variants with increased Hb A2 levels and/or co-migration with Hb F are associated with a high proportion of mis-interpretation of β-thalassemia in routine practice.