Q. A 52-year-old Caucasian male presents to the outpatient clinic with complaints of persistent diarrhea, unexplained weight loss, and worsening fatigue over the past six months. Despite adhering strictly to a gluten-free diet for the past three years since his diagnosis of celiac disease, his symptoms have been increasing in intensity. On physical examination, he appears generally malnourished and has evidence of pallor. His body mass index is 18 kg/m². Upon abdominal examination, there is slight diffuse tenderness but no distension, masses, or organomegaly noted. Laboratory investigations reveal a hemoglobin of 9.8 g/dL, mean corpuscular volume (MCV) of 72 fL, serum ferritin of 15 ng/mL, and total serum protein of 6.0 g/dL. Stool microscopy and culture are normal. A repeated serology for celiac disease showed elevated IgA tissue transglutaminase (tTG) antibodies of 42 U/mL and endomysial antibodies of 1:80 titers. What is the most appropriate next step in the management of a patient's condition?