Le expired hydrogen test (or breath test) is used to diagnose a digestion problem sugars in the intestine.

Sometimes called lactose sensitivity test, it consists in detecting the presence and amount of hydrogen in exhaled air.

The principle is simple: if it is difficult to digest sugars such as lactose (a sugar found in dairy products), it turns into gas (hydrogen) in the intestine, under the action of intestinal bacteria (i.e. is fermentation).

The hydrogen thus produced passes into the bloodstream and reaches the lungs, to be exhaled at the same time as the air. The more hydrogen in the exhaled air, the less efficient the lactose digestion.

The test can also detect an abnormality in the digestion of other sugars, such as glucose or fructose. It is a simple and non-invasive test.

The test makes it possible to diagnose a problem with the digestion of certain sugars:

• le lactose : to confirm poor digestion of dairy products (lactose intolerance)
• le fructose : to confirm poor digestion of fructose, the main sugar contained in fruits (fructose intolerance)
• le sucrose (very rare)

The doctor may order an exhaled hydrogen test for various digestive symptoms, such as bloating, flatulence, abdominal pain, digestive disorders (diarrhea, vomiting, etc.)

The test can also be used when one wants to measure the orocecal transit time or to look for an bacterial overgrowth in the intestine (excessive number of bacteria in the small intestine). The patient will then be administered specific sugars during the examination, such as lactulose or glucose, before their exhaled hydrogen level is measured.

Note that in the event of a suspicion of fructose or lactose intolerance, the first step is often to completely exclude these sugars from the diet, in order to see if the symptoms are alleviated or not. This diet is often sufficient to make the diagnosis.