To the Editor.
—The message of the article by Hansen et al1 and Howe's2 accompanying editorial in the January issue of the Archives is sobering. During the last decade, not only have electronic counters made the traditional red blood cell counts and indices more reliable for detecting iron deficiency and thalassemia3,4 but new indices, such as the red blood cell distribution width (RDW), are now widely available. The RDW improves the distinction between iron deficiency and heterozygous thalassemia when mean corpuscular volume (MCV) is low5-7 and between iron-deficient and normal subjects when MCV is normal.8 However, in view of the data of Hansen et al, it is unlikely that physicians who do not use the long-established MCV will do much better with the additional information given by the RDW. We share the view that the diagnostic approach to microcytic anemias needs to be improved.Incidentally,