Discriminant value of % microcytic/% hypochromic ratio in the differential diagnosis of microcytic anemia

BACKGROUND: % Microcytic and % hypochromic red cells show an inverse trend in beta thalassemia trait and in iron deficiency anemia (IDA). The aim of this study was to assess the discriminant value of % microcytic/% hypochromic ratio, as can be obtained from the Advia 2120 (Siemens) analyzer, in the differential diagnosis of microcytic anemia, compared to the conventional England and Fraser, Green and King, Mentzer, Ricerca, Shine and Lal and Srivastava indices. METHODS: Receiver operating characteristic (ROC) curves, sensitivity, specificity and Youden index of indices were calculated for a set of 148 IDA patients and 170 beta thalassemia carriers. RESULTS: The Green and King index showed the best area under the curve (AUC, 0.962), with a Youden index of 80.9%; the % microcytic/% hypochromic ratio ranked second (AUC 0.943), with a Youden index of 76.3% and a sensitivity of 99.2%. CONCLUSIONS: This index, with high sensitivity for beta thalassemia screening, can be a useful tool in the differential diagnosis of microcytic anemia, so samples can be chosen for HbA(2) analysis, to confirm the presumptive diagnosis of the disease. As specificity is 77.1%, we assume it will be 22.9% for false positives, but these samples will have HbA(2) values within the reference range, for correct diagnosis.