Assessment of the Matos & Carvalho index for distinguishing thalassemia from iron deficiency anemia

In a recent issue of this journal, Matos et al. proposed a new index for discriminating between iron deficiency anemia (IDA) and the thalassemia trait.1 We read their paper with great interest, since we have performed similar research in this field.2 Recently we completed a study in which we compared 25 discriminant formulas incorporating only basic red blood cell (RBC) parameters using a large database of patients with mild microcytic anemia, who either had a diagnosis of IDA or were thalassemia carriers.3 This database now gives us the opportunity to investigate the diagnostic performance of the Matos & Carvalho (M&C) index in a much larger patient cohort than the authors used for their development and validation,1 and we present our findings in this communication. Our database comprises 2664 patients with microcytic anemia, defined as hemoglobin <13 g/dL and mean corpuscular volume (MCV) <80 fL, irrespective of gender. It was built over a period of nine years, during which time the Beckman Coulter LH780 was the main hematology analyzer in use; other hematology analyzers were operated for shorter periods. Standard biochemical and hematological methods were used to make the diagnosis; the diagnosis of -thalassemia was based on molecular techniques. Of our patients, 1196 had “pure” thalassemia (319 -thalassemia and 877 -thalassemia), 1259 had simple IDA, 117 had thalassemia with concomitant IDA, 33 had thalassemia with concurrent anemia of chronic disease, 23 had complex thalassemia and 36 had other diseases associated with microcytic anemia. When applying the M&C formula to our database in the receiver operating characteristic (ROC) analysis, we found an area under the curve (AUC) of 0.892 (95% confidence interval: 0.879–0.904); as Figure 1 demonstrates this AUC is significantly (p-value < 0.0001) lower than the three best performing formulas in our study that all had AUCs around 0.95.3 At the optimal cut-off of 23.6, the M&C index resulted in 0.854 sensitivity, 0.795 specificity and a Youden index of 0.649. If we had included the M&C index in our study, then it would have