A 30-year-old woman presents with a 6-month history of chronic diarrhea, bloating, and unintentional weight loss. She also reports fatigue and has been found to have iron-deficiency anemia refractory to oral iron supplementation. Laboratory tests reveal positive anti-tissue transglutaminase (tTG) IgA antibodies and elevated total IgA. What is the most appropriate next step to confirm the diagnosis?

The correct answer to the question "A 30-year-old woman presents with a 6-month history of chronic diarrhea, bloating, and unintentional weight loss. She also reports fatigue and has been found to have iron-deficiency anemia refractory to oral iron supplementation. Laboratory tests reveal positive anti-tissue transglutaminase (tTG) IgA antibodies and elevated total IgA. What is the most appropriate next step to confirm the diagnosis?" is Option B: Perform an upper endoscopy with duodenal biopsies.

The other options — A) Initiate a gluten-free diet and reassess symptoms, C) Order stool studies for ova and parasites and Clostridium difficile, D) Consult genetics for HLA-DQ2/DQ8 testing — are incorrect for this USMLE Exam Prep question. As explained above: While serology (positive anti-tTG IgA) is highly suggestive of celiac disease in a symptomatic patient, definitive diagnosis requires characteristic histological changes on duodenal biopsies obtained…