To the Editor: We read with interest the paper (1) by Beyan et al. concerning the discrimination between b-thalassemic trait (bTT) and iron deficiency anemia (IDA) with the aid of indices based on red blood cell parameters. In particular, they incorporated red blood cell count (RBC), red blood cell distribution width (RDW), Mentzer index, Shine and Lal index, England and Fraser index (E&F), Srivastava index, Green and King index (G&K), RDW index and Ricerca index. This study was conducted simultaneously with our study which focused on a Greek adult population and included six of the aforementioned indices (2). In Beyan’s study, the most reliable index was RBC, which was the third more powerful index in our study. On the other hand, in our study G&K was the most accurate, which ranked second in the study by Beyan et al. Both studies strongly concluded that none of the indices can be relied on for a safe differential diagnosis between b-TT and IDA, as Youden index was only 73.7% and 70.8% respectively. Moreover, sensitivity for diagnosis of b-TT was only 84.8% and 75% respectively, suggesting that these indices cannot even be used as a screening tool for b-TT, as they could result in a significant number of false negative results. The fact that the two studies did not coincide on which one is the most accurate index may be explained by the different sample size which was much larger in our study (111 vs. 493 patients). Another reason may be the fact that Beyan et al. excluded IDA patients with haemoglobin levels lower than 8.7 mg ⁄ dL. The results of these two papers confirm previous work by Demir et al. in a study conducted in a paediatric population (3). In this case, the authors studied 63 children and concluded that no index was reliable in the differential diagnosis between b-TT and IDA. They found that the most reliable index was RBC, for which Youden index was only 82%. However, in a recent study (4) by Alfadhli et al., the authors concluded that E&F is highly reliable in distinguishing b-TT from IDA. In particular, they studied 103 patients and found that in the case of E&F, Youden index was 98.2%. On an attempt to explain the different results compared with Demir’s study, the authors suggested that these may be caused by the different sample size (63 in Demir’s study compared with 103 in Alfadhli’s study), as well as by the different mean age ( 16 yr respectively). However, if we compare the Alfadhli’s study with both Beyan’s and our study, these differences do not exist, as all patients were >16 yr and the sample size was 103, 111 and 493 respectively. That means that there may be a different explanation for the results in Alfadhli’s study, other than the sample size and age of the patients. Thus, we still believe that the aforementioned indices cannot provide a safe diagnostic tool for the discrimination between b-TT and IDA.