Primary hypolactasia diagnosis: Comparison between the gaxilose test, shortened lactose tolerance test, and clinical parameters corresponding to the C/T-13910 polymorphism.

Summary Background & aims There is no consensus on the most accurate method to diagnose primary hypolactasia. We aimed to compare the diagnostic accuracy of the new gaxilose test with 2 traditional tests (lactose tolerance test and clinical criteria) for the diagnosis of primary hypolactasia using the C/T-13910 polymorphism as a reference standard. Methods Patients with a clinical suspicion of lactose intolerance were subjected to gaxilose tests, shortened lactose tolerance tests, and symptom questionnaires before and after overload with 50 g lactose and after a lactose-free diet. The diagnostic accuracy and degree of agreement and correlation were assessed using a genetic test (C/T-13910 polymorphism) as a reference standard and their respective 95% confidence intervals. Results Thirty consecutive patients (70% women) participated in the study. The genetic test confirmed the C/T-13910 polymorphism in 11 patients (36.8%). The presence of diarrhoea and the symptom score after lactose overload, along with the tolerance test, were the variables with the highest degree of agreement ( κ  > 0.60). Area under the ROC curve was >0.82 ( p 0.80. However, the gaxilose test obtained lower values: κ , 0.47; area under curve, 0.75 (0.57–0.94); sensitivity, 0.82 (0.55–1); and specificity, 0.68 (0.45–0.92). The multivariate analysis showed an association between the post-overload symptom questionnaire and the results of the genetic test (odds ratio: 1.17; 1.04–1.31; p Conclusions The presence of diarrhoea and the symptom score after overload with 50 g lactose showed a higher degree of agreement and diagnostic accuracy for primary hypolactasia than the gaxilose test when the genetic test is used as a reference standard.