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 < 0.05), with sensitivity and specificity values of >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 < 0.01).
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.
Keywords: Gaxilose test; Hypolactasia; Lactose intolerance diagnosis; Lactose malabsorption.
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