Red cell indices: differentiation between β-thalassemia trait and iron deficiency anemia and application to sickle cell disease and sickle cell thalassemia

Background: In Tunisia, thalassemia and sickle cell disease (SS) represent the most prevalent monogenic hemoglobin disorders with 2.21% and 1.89% of carriers, respectively. This study aims to evaluate the diagnosis reliability of 12 red blood cell (RBC) indices in differentiation of beta-thalassemia trait (beta-TT) from iron deficiency anemia (IDA) and between homozygous SS and sickle cell thalassemia (ST). Methods: The study covered 384 patients divided into three groups. The first one is composed of 145 control group, the second consists of 57 beta-TT and 52 IDA subjects and the last one with 88 SS and 42 ST patients. We calculated sensitivity, specificity, positive-predictive values, negative-predictive values, percentage of correctly identified patients and Youden's Index (YI) for each indice. We also established new cut-off values by receiver operating characteristic curves for each indice. An evaluation study was performed on another population composed of 106 beta-TT, 125 IDA, 31 SS, and 17 ST patients. Results: Srivastava Index (SI) shows the highest reliability in discriminating beta-TT from IDA at 5.17 as a cut-off and also SS from ST with 7.7 as another threshold. Mentzer Index (MI) and RBC appear also useful in both groups with new cut-offs slightly different from those described in literature for beta-TT and IDA. Conclusions: The effectiveness and the simplicity of calculation of these indices make them acceptable and easy to use. They can be relied on for differential diagnosis and even for diagnosis of beta-TT with atypical HbA(2) levels.