Iron deficiency anemia can be caused by either decreased iron availability or increased iron requirements after blood loss from the gastrointestinal (GI) tract. Nabil M. Abou Baker, MD, and Andrew M. Davis, MD, MPH, both of the University of Chicago, join JAMA Deputy Editor Michael Berkwits, MD, MSCE, to discuss the evaluation of iron deficiency anemia and 2020 AGA recommendations for the workup of GI causes, including revised thresholds for ferritin values and the use of upper and lower (bidirectional) endoscopy. Related Content: Gastrointestinal Evaluation of Iron Deficiency Anemia