The ratio of the mean corpuscular volume (MCV) and red blood cell count (RBC) can be automatically calculated with any of the newer hematology analyzers.METHODS: The results of 398 patient screens were collected. Data from the set were divided into training and validation subsets. The Mentzer ratio was determined through a receiver operating characteristic (ROC) curve on the first subset, and screened for thalassemia using the second subset.