The Evaluation of Various Mathematical RBC Indices and Their Efficacy in Discriminating Between Thalassemic and Non-Thalassemic Microcytosis

The differentiation between thalassemic and non-thalassemic microcytosis has important clinical implications in hematology and medicine. A simplified index, based on red cell parameters derived from automated blood cell analyzers, which could be used to discriminate between microcytic patients with a high probability of thalassemia minor and those with a low probability, would be an extremely useful tool. Five mathematical indices have been proposed as useful for this purpose. These are the: Bessman index, Shine and Lal index, England index, Mentzler index, and mean cell volume (MCV) alone. This study was designed to prospectively evaluate the efficacy of these indices. Patient samples were chosen every fourth day from all patient samples referred to the hematology laboratory at St. Joseph's Hospital over a 6-month period. All patient samples with an MCV < 80 fL and age > or = 18 years were considered eligible for the study. After enrollment and laboratory analysis were complete sensitivities and specificities were calculated for each of the indices using a variety of cut-off values and receiver operator characteristic (ROC) curves were constructed. Based on statistical analysis of the area under these curves, the authors conclude that MCV alone is as effective as the Mentzler and Shine and Lal indices in selecting microcytic patient samples with a high probability of thalassemia minor for thalassemia testing. They also conclude that the Bessman index and the England index are ineffective indices for this purpose.