The C-13/H-2-glucose test for determination of small intestinal lactase activity

Background To diagnose hypolactasia, determination of lactase enzyme activity in small intestinal biopsy material is considered to be the golden standard. Because of its strongly invasive character and the sampling problems, alternative methods have been looked for.Design We analysed the C-13-glucose response in serum after consumption of 25 g of naturally enriched C-13-lactose. As an internal standard, 0.5 g of H-2-glucose was added and the H-2-glucose response in serum was measured simultaneously. The studies were performed in healthy volunteers with a background of genetically determined lactase nonpersistence (n = 12; low lactase activity) and lactase persistence (n = 27; high lactase activity). The results were compared with those of the lactose hydrogen breath test, the lactose (CO2)-C-13 breath test and the previously described C-13-lactose digestion test.Results After consumption of C-13-lactose and H-2-glucose, the mean ratio C-13-glucose/H-2-glucose concentration in serum at 45-75 min was 0.26 +/- 0.09 in the low lactase activity group and 0.93 +/- 0.17 in the high lactase activity group (P <0.01). Threshold of the ratio between digesters and maldigesters was calculated as 0.46. Accuracy of the new test was superior to all other tests.Conclusions We conclude that the C-13/H-2-glucose test has the potential of determining the small intestinal lactase activity in vivo and of estimating the amount of lactose which is digested in the small intestine.