Lactose is a disaccharide formed by two sugars: glucose and galactose. It is the principle carbohydrate contained in mammal milk. In human milk it has a presence of about 7%. A correct digestion of lactose depends on the presence in the intestine of the LACTASE enzyme that splits it into the two easily digestible carbohydrates: glucose and galactose. As well as in milk, lactose is present in all its derivative forms: dairy products, cheese, custard, cream, ice cream, etc.
Lactose intolerance, or more correctly, lactose mal-digestion, is a condition characterised by gastro-intestinal disorders that arise after ingestion of foods containing this sugar, generated by a weak production by the duodenum intestinal cells of the lactase enzyme and the breakdown of lactose into glucose and galactose that in this form can be absorbed. This is not, as sometimes referred to, an allergy: eventual milk allergies are actually supported by particular proteins contained in milk. Lactose intolerance is the more common form of mal-absorption of carbohydrates and affects people of all ages. The intolerance is manifested in many people, often unaware of the cause of their suffering, with a series of gastro-intestinal disorders that can often mislead the doctor, resulting in inappropriate prescription as a consequence of the lack of a precise lactose intolerance diagnosis.
Diagnosis is possible through a breath test and duodenal biopsy and through specific blood tests. A form of “transitory” lactose intolerance exists, particularly frequent in paediatric age. In these cases, a primitive cause (for example infective gastroenteritis) can cause a temporary lactose deficit. For this reason it is good practice in paediatrics to avoid administering milk on the first day of gastroenteritis as being a lactase deficit the undigested lactose may worsen the diarrhoea. The therapy is dietary and requires a reduction or total exclusion of foods containing lactose in the diet.
The H2 Breath Test is a technique with many applications, such as the study of ideal absorption capacity, oral-caecal transit and pancreatic function, which are actually little known. This test is frequently included in investigations carried out to diagnose intolerance to certain carbohydrates. In normal conditions after ingestion lactose splits from the intestinal lactase into glucose and galactose that are then absorbed into the small-bowel; if there is a shortage of lactase, the lactose reaches the colon unaltered where it gets fermented by the bacterial flora producing various gasses among which hydrogen and carbon dioxide which in part pass into the blood circulation and are eliminated through the air in the lungs. This is the principle on which the hydrogen Breath Test is based. With the H2 Breath Test the quantity of hydrogen breathed present in alveolar air is measured by this test.
The test can be useful in those patients who report gastroenterological upsets such as flatulence, trapped wind, diarrhoea, abdominal distension and cramps following the ingestion of milk and its derivatives.
The test consists of a collection of breathed air samples, before and after ingestion of one specific sugar dissolved in water (lactose), into a plastic bag at regular intervals. The test lasts four hours.
The test is carried out nil-by-mouth (empty stomach)
The day before the exam the patient must diet exclusively on:
| Breakfast: | a cup of tea |
| Lunch: | a plate of boiled rice dressed with a little oil |
| Dinner: | chicken breast/grilled or poached turkey/poached fish |
During the test, the patient must ingest a specific quantity of lactose and then breathe into a bag in the subsequent 3 hours thereby producing air samples. The breathed air is then measured for the quantity of hydrogen it contains. In the case of lactose mal-absorption, after the ingestion of lactose and in absence of the enzyme that it must metabolise (lactase) , processes of fermentation take place in the intestine and the production of hydrogen increases, which is absorbed into the circulation and eliminated through the lungs via breath. The increase, compared to baseline values, of the production of gas from the ingestion of lactose indicates that the subject is intolerant to lactose. The test is considered positive when a peak of hydrogen registered in the breathed air is superior to the baseline values registered on arrival in the laboratory. Otherwise, the test is considered negative. Finally, based on the scale of the peak, the lactose intolerance can be classified as light, severe or moderate.
