Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (153 page)

   Oral sucrose tolerance curve is flat, but glucose plus fructose tolerance test is normal. Occasionally, there is an associated malabsorption with increased stool fat and abnormal
D
-xylose tolerance test, although intestinal biopsy is normal.

   Hydrogen breath test after sucrose challenge.

   Intestinal biopsy with measurement of disaccharidase activities.

   Sucrose-free diet causes cessation of diarrhea.

   Glucose–galactose malabsorption (inherited autosomal recessive defect that affects the kidney and intestine)

   Oral glucose or galactose tolerance curve is flat, but IV tolerance curves are normal.

   Glucosuria is common. Fructose tolerance test is normal.

   Secondary malabsorption

   Resection of >50% of the colon disaccharidase activity. Lactose is most marked, but there may also be sucrose. Oral disaccharide tolerance (especially lactose) is abnormal, but intestinal histology and enzyme activity are normal.

   Diffuse intestinal disease—especially celiac disease in which activity of all disaccharidases may be decreased, with later increase as intestine becomes normal on gluten-free diet; also cystic fibrosis of the pancreas, severe malnutrition, UC, severe
Giardia
infestation, blind loop syndrome, β-lipoprotein deficiency, effect of drugs (e.g., colchicine, neomycin, birth control pills). Oral tolerance tests (especially lactose) are frequently abnormal, with later return to normal with gluten-free diet. Tolerance tests with monosaccharides may also be abnormal because of defect in absorption as well as digestion.

   Small intestinal bacterial overgrowth (see Figure
5-4
)

   Quantitative aerobic and anaerobic culture of aspirate of small bowel content showing >10
⁵
cfu/mL of anaerobic organisms is considered diagnostic. The utility of culture is limited, however, because it requires invasive collection; there may be sampling error due to limited regions of involvement within the small bowel, and culture techniques and interpretation are not standardized.