Chronic diarrhea with weight loss: interpret the malabsorption work-up

Same patient: a 24-year-old woman with 4 months of bulky, floating, foul-smelling stools, bloating and weight loss. Her results are below. Interpret them, give the diagnosis and outline the next steps and management.

CBC: Hb 10.1 g/dL (female reference 12-16), MCV 74 fL (80-100). Serum calcium low.

Stool: Sudan stain positive; 72-hour fecal fat 15 g/day on a fat intake of 80 g/day. Fecal elastase normal. Stool culture negative.

D-xylose test: low serum and urine xylose levels.

Serology: tTG-IgA strongly positive. Total serum IgA normal.