Discriminant indices for distinguishing thalassemia and iron deficiency in patients with microcytic anemia: a meta-analysis

Background: More than 40 mathematical indices have been proposed in the hematological literature for discriminating between iron deficiency anemia and thalassemia trait in subjects with microcytic red blood cells (RBCs). None of these discriminant indices is 100% sensitive and specific and also the ranking of the discriminant indices is not consistent. Therefore, we decided to conduct the first meta-analysis of the most frequently used discriminant indices. Methods: An extensive literature search yielded 99 articles dealing with 12 indices that were investigated five or more times. For each discriminant index we calculated the diagnostic odds ratio (DOR) and summary ROC analysis was done for comparing the performance of the indices. Results: The ratio of microcytic to hypochromic RBCs (M/H ratio) showed the best performance, DOR = 100.8. This was significantly higher than that of all other indices investigated. The RBC index scored second (DOR = 47.0), closely followed by the Sirdah index (DOR = 46.7) and the Ehsani index (DOR = 44.7). Subsequently, there was a group of four indices with intermediate and three with lower DOR. The lowest performance (DOR = 6.8) was found for the RDW (Bessman index). Overall, the indices performed better for adults than for children. Conclusions: The M/H ratio outperformed all other discriminant indices for discriminating between iron deficiency anemia and thalassemia trait. Although its sensitivity and specificity are not high enough for making a definitive diagnosis, it is certainly of value for identifying those subjects with microcytic RBC in whom diagnostic tests for confirming thalassemia are indicated.