Breath tests can be helpful in the evaluation of bloating, diarrhoea, constipation and malabsorption. These tests are safe alternatives to more invasive procedures such as biopsy. According to research from the 1970s, which was repeated in 2006 , approximately 35% of healthy adult subjects are methane producers. It was also reported  that, in 34% of lactose intolerant patients with a negative hydrogen breath test, the methane percentage increase after a lactose challenge was greater than 100%. In the same study, out of 13 subjects with a false negative breath hydrogen response to lactulose, 11 subjects had a methane percentage increase greater than 100%. Methanogenic bacteria are independent of hydrogen-producing bacteria; so methane determination along with the measurement of hydrogen is thus required in the study of lactose intolerance  and in other carbohydrate breath tests.
This test is sold for self-administering at home and returning the sample by post.
The patient should not have eaten slowly digesting foods such as beans and bran on the day before the test and should have fasted for 14 hours prior to the test, with only water to drink. Vigorous exercise, smoking or sleeping should be avoided immediately before, or at any time during the test.
For the lactulose breath test the patient is given 10 gm of lactulose syrup with 200 ml of water; alveolar air samples are collected at baseline and then every 20 minutes for 3 hours (a total of 10 samples). If the result is equivocal, it is recommended that the test should be repeated using 40 gm of lactulose.
Home collection breath tubes stable for at least 14 days after collection