EVALUATION OF (CO2)-C-13 BREATH TESTS FOR THE DETECTION OF FRUCTOSE MALABSORPTION

Breath hydrogen (H-2) studies have made clear that small intestinal ab sorption of fructose is limited, especially in toddlers. Malabsorption of fructose may be a cause of recurrent abdominal pain and chronic no nspecific diarrhea (toddler's diarrhea). Fructose absorption is facili tated by equimolar doses of glucose and, as we have found, amino acids (especially L-alanine); the mechanism underlying this effect remains unclear. To study fructose absorption in a more direct way, we combine d breath H-2, studies with breath (CO2)-C-13 studies. Gastric emptying was studied by using L-glycine-1-C-13 in 4 children from 12.1 to 16.0 years of age. After 25 gm of fructose and 27.5 gm of glucose, when gi ven together, gastric emptying was significantly (p < 0.05) slower tha n with either sugar alone. In a second series of experiments, 5 childr en from 12.0 to 15.9 years of age were tested with 25 gm of fructose, alone and with equimolar doses of glucose and L-alanine, and 4 younger children from 3.1 to 6.1 years of age were tested with 2 gm/kg (max 3 7.5 gm) fructose, alone or with an equimolar dose of L-alanine. All fr uctose solutions were enriched with 15 mg of D-fructose-C-13-6. In all 9 children, fructose was malabsorbed as judged by breath H-2 increase s greater than or equal to 20 ppm, and the addition of glucose or L-al anine resulted in significantly lower breath H-2 increases (p less tha n or equal to 0.005 for glucose, p less than or equal to 0.001 for ala nine). In contrast, the addition of alanine or glucose did not change the pattern of breath (CO2)-C-13 excretion in the 5 older children, wh ereas in the 4 younger children (with relatively higher doses), L-alan ine addition resulted in significantly lower increases in breath (CO2) -C-13. In the tatter group, for each time point, breath H-2 and (CO2)- C-13 concentrations after fructose were compared with those after fruc tose plus L-alanine; in 20 out of 24 points, both H-2 and (CO2)-C-13 w ere higher after fructose. These results suggest that (CO2)-C-13 not o nly originated from the oxidation of absorbed substrate but also, at l east in part, from colonic bacterial metabolism. For the detection or fructose malabsorption-as opposed to, for instance, lactose-the (CO2)- C-13 breath test seems to be of limited value.