Goals and Background: Hypolactasia affects over half of the world population. Diagnosis remains problematic as currently available tests, such as the hydrogen breath test, have low reliability and lactose intolerance symptoms are unspecific. We evaluated the diagnostic performance and safety of a new noninvasive diagnostic test based on urine or serum measurement of D-xylose after lactase cleavage of orally administered 4-galactosylxylose (gaxilose).
Study: In a multicentre, open-label, nonrandomized, phase IIb-III study, consecutive patients with symptoms suggestive of lactose intolerance sequentially underwent intestinal biopsy for direct measurement of lactase activity (reference standard), hydrogen breath test, and blood glucose test after lactose challenge, 4- and 5-hour urine-based gaxilose test, and blood-based gaxilose test. For the gaxilose tests, 0 to 4 and 4 to 5 hours urine samples were taken after a 0.45 g gaxilose dose, whereas serum samples were taken 90 minutes after a 2.7 g dose for D-xylose determination. Genetic testing of hypolactasia was also assessed.
Results: Of the 222 patients enrolled, 203 completed all diagnostic tests; 108 were hypolactasic according to biopsy. The sensitivities and specificities and positive and negative predictive values of the gaxilose tests were all >90% versus 69% to 85% for the hydrogen breath test and the blood glucose test. The area under the ROC curve was significantly higher for the gaxilose tests (>0.9, P≤0.007). These tests also had higher sensitivity than genetic testing for hypolactasia and were well tolerated.
Conclusions: The diagnostic performance of the gaxilose tests is excellent and can substantially improve the diagnosis of hypolactasia.