For a more quantitative measurement of fat absorption, a 72-h fecal fat collection frequently is helpful in documenting steatorrhea. Oral tolerance tests Excretion of breath hydrogen, a product of bacterial fermentation of unabsorbed lactose, often is elevated in celiac sprue. The oral D-xylose tolerance test can reveal carbohydrate malabsorption. D-xylose is absorbed preferentially in the proximal small intestine and excreted in the urine unmetabolized. In untreated celiac sprue, urinary D-xylose excretion and peak blood xylose levels are depressed.
Lactose tolerance is another oral tolerance test.
The serum IgA antigliadin antibody is more specific but less sensitive than the serum IgG antigliadin antibody. The presence of serum IgA antibody to endomysium in untreated celiac sprue has higher sensitivity and specificity than antigliadin antibodies. However, serum IgA antiendomysial antibody often becomes undetectable after 6-12 mo of gluten withdrawal. Small bowel barium studies X-ray evaluation of the small bowel after barium ingestion is helpful in making a diagnosis of untreated celiac sprue. Abnormal findings can include dilatation of the small intestine, a coarsening or obliteration of the normally delicate mucosal pattern, and fragmentation or flocculation of the barium in the gut lumen.