The purpose of this study is to evaluate both the impact of LacTEST on diagnostic thinking and on patient management, and its reproducibility (Test-Retest), for the diagnosis of hypolactasia in adults and elderly patients presenting with clinical symptoms of lactose intolerance.

Inclusion Criteria:

1. Adults of either sex, between 18 and 70 years old.
2. Capacity for understanding and giving the informed consent to participate in this study.
3. Patients with clinical suggestive of lactose intolerance, primary or secondary, who have not been diagnosed and that fulfil the requirements allowed by the gaxilose summary of product characteristics (SmPC).

Exclusion Criteria:

1. Pregnant women or breast-feeding women.
2. Unable or reticent to give the informed consent or to comply with the study requirements.
3. Patients with glomerular filtration rate (GFR) less than 90 ml/min/1.73m2.
4. Portal hypertension: ascites, cirrhosis.
5. Medical records of total gastrectomy and/or vagotomy.
6. Patients diagnosed with myxedema.
7. Patients with Diabetes Mellitus.
8. Patients who are participating or have participated in any clinical trial within the 3 months previous to their inclusion in the study.
9. Patients who are drug abuse consumers.
10. Patients under treatment with antibiotics, sulphamides and antiparasitics, who cannot suspend the treatments 7 days prior to the performance of the hydrogen breath test.
11. Patients with any recognized and already existing disorder that might interfere with the any of the lactose intolerance diagnosis tests.
12. Patients who have taken aspirin of indomethacin in the 48h preceding the performance of the Gaxilose test.