IBS Fact : Evidence-based management of irritable bowel syndrome

Testing for lactose intolerance

Lactose intolerance is the inability to digest lactose, the natural sugar in milk and dairy products. When undigested lactose enters the large intestine, it becomes fermented by intestinal bacteria causing symptoms such as flatulence, abdominal cramping, and diarrhoea. Since these symptoms are similar to those of IBS, a lactose intolerance test is often used to distinguish between the two conditions. Interestingly, the intestinal fermentation of undigested lactose also produces small amounts of hydrogen, which can be detected in the breath. Hence, by consuming a specific amount of lactose and subsequently measuring hydrogen in the breath, lactose intolerance can be measured, which is the principle of the hydrogen breath text.

Preparation for the test consists of eliminating any digestive processes or substances that may interfere with the measurement. This involves an overnight fast and abstaining from any liquids eight hours prior to the test. Smoking and certain antibiotics or drugs may also need to be discontinued. The actual test consists of collecting breath samples by blowing into a bag or tube, which are then introduced in the device measuring the hydrogen. The protocol starts with a baseline sample to determine the fasting level of breath hydrogen. A lactose-containing liquid is then ingested, and the breath is sampled again at intervals of 15 minutes for up to 2 hours. Once measurements are complete, the data are analysed and results discussed, either immediately or at a later time. Daily activities can be resumed immediately after completing the test as no drugs are involved. If results indicate lactose intolerance, the next step will consist of avoiding diary and milk products. This should resolve intestinal symptoms within 24-72 hours. If symptoms persist despite a lactose-free diet, additional tests may be required to determine if another condition, such as IBS, may also be involved. In case of negative results, i.e. no lactose insufficiency, and no improvement of symptoms when abstaining from diary products, the diagnosis of IBS may be made in conjunction with additional examinations.

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