**1. Introduction**

246 New Advances in the Basic and Clinical Gastroenterology

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Clinicians are traditionally taught that the differential diagnosis of microcytic anemia is limited to a very few causes, with iron deficiency anemia on top of that list. While this may be true, the specific etiology of these causes and specifically the exact cause of the iron deficiency in each case is of clinical importance, as treatment of the anemia is very different for each cause. Just as the most common reason for severe microcytic anemia at any age is iron deficiency, the most common reasons for that deficiency at any age involve the gastrointestinal tract. The gastrointestinal tract is both the site of iron uptake and the most common site of blood loss. Thus, the gastrointestinal specialist plays a key role in diagnosing and managing microcytic anemia and must understand the various etiologies of microcytic anemia that are likely or possible in the population seen, including those cases that do not have a GI cause. In this chapter we will explain in a case based format the proper workup of the child and adolescent with microcytic anemia, emphasizing the role of the GI tract in the mechanism and of the GI specialist in the diagnosis and management.
