Lactose intolerance test: the Breath Hydrogen Test

The Breath Hydrogen Test (BHT) is a test to assess the intestinal digestion of lactose (milk sugar) and to detect lactose intolerance, a syndrome defined by the inability of intestinal cells to break down lactose into simple sugars (glucose and galactose) due to a deficiency in the enzyme lactase.

How does the BHT work?

This is the most commonly used test for the definite diagnosis of lactose intolerance, it takes 3 to 4 hours, is reliable and very specific and is risk-free. Several conditions must be met before the test is carried out: it is recommended not to use antibiotics two to four weeks before the test and laxatives three days before the test. The day before the test, no milk, fruit juices or foods that cause the production of intestinal gas, such as starchy foods and cabbage, should be consumed. The patient must fast for at least 6 hours before the test, but may drink water at any time.

After taking in 10-50 g of lactose or 200-350 ml of cow's milk, the person exhales into a mouthpiece every 30 minutes to measure the amount of hydrogen exhaled.

What is the purpose of this test?

The principle of the test is simple, lactose is poorly digested in the intestine and undergoes fermentation by bacteria in the colon, resulting in the hyperproduction of hydrogen, which passes into the bloodstream and reaches the lungs. Patients at rest do not produce hydrogen, so any increase in the level of hydrogen exhaled is necessarily due to this fermentation. The more hydrogen in the exhaled air, the greater the lactase deficiency. In very rare cases, the bacteria in the colon do not produce hydrogen, even in cases of lactose intolerance.

The doctor may prescribe a hydrogen-exhalation test in case of various digestive symptoms, such as bloating, abdominal pain, transit disorders (diarrhoea, vomiting) or also in case of suspected intolerance to other sugars such as glucose or fructose (fruit sugar).

It should be noted that in case of suspected lactose intolerance, the first step is to proceed with a complete exclusion of foods containing lactose for 3 days in order to see if the symptoms improve or not, this is the eviction test. The eviction test is not necessary in the case of irritable bowel syndrome or in the case of a known intestinal disease.

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