ABOUT THE TEST The test consists of administering a lactose solution orally and collecting the exhaled air at different times. (each 30 minutes), to determine the amount of hydrogen and/or methane exhaled through the breath. The total duration of the test is 3 hours and a half (210 minutes). Under normal conditions, lactose is absorbed in the small intestine.. If there is insufficient absorption of lactose due to an enzyme deficiency, This reaches the large intestine where it is fermented by resident bacteria., producing gases (hydrogen and/or methane) which are partially absorbed by the blood and expelled through the breath. Thus, according to the results obtained of hydrogen and/or methane exhaled for each intake, we can detect a possible lactose intolerance. To interpret the results you should go to a specialist who knows your clinical situation., This being essential in the event that any of the results are positive.