Discrimination Indices as Screening Tests for Beta-Thalassemic Trait.

Introduction: The two most frequent microcytic anemias are β-thalassemic trait (β-TT) and iron deficiency anemia (IDA). Several discrimination indices have been proposed in order to distinguish between these two conditions. These indices are derived from several simple red blood cell indices, like RBC count, mean cell volume and RBC distribution width (RDW), as these are provided by electronic cell counters. Purpose of the study is to examine the diagnostic accuracy of six discrimination indices in the differentiation between IDA and β-TT.

Methods: The six discrimination indices that were examined were: Mentzer Index, Green & King Index, RDW Index, England & Fraser Index, RDW and RBC count. We calculated these indices on 373 patients (205 males, 168 females) with β-TT and 120 patients (50 males, 70 females) with IDA, as well as their sensitivity, specificity, positive and negative prognostic value, efficiency and Youden’s index.

Results: G&K shows the highest reliability, followed by E&F, RBC count, MI and RDWI. On the contrary, RDW completely failed to differentiate between IDA and β-TT. G & K proved to be the most reliable index, since it had the highest sensitivity (75.06%), efficiency (80.12%) and YI (70.86%) for the detection of β-TT.

Conclusion: These six discrimination indices cannot be relied on for a safe differential diagnosis between β-TT and IDA. They do have high specificity, but their sensitivity for the detection of β-TT is not satisfactory. Consequently, they cannot be used neither as a screening tool for β-thalassemic trait, since they could result in a significant number of false negative results.