A previous study reported the FRC count to be falsely high in samples taken from patients with microcytic anaemia.16 We then analysed the correlation between the difference in schistocyte measurements and Hb specifically in the group of patients with thalassaemia trait and disease, because both conditions have microcytic RBCs.28 The correlation was also found to be poor (rs = 0.051) (95% CI, −0.287 to 0.378, P = 0.77) (see Figure S1 in the Supplementary information). This evidence concerns the gene GSTM1 and thalassemia.