This is a non-invasive way for looking for sugar malabsorption of various types.
These take several hours and need to be done fasting. This is because a drink involving an amount of the sugar to be tested for such as sucrose or lactose will be drunk and then if this is not absorbed properly into the gut it will be passed through into the large bowel where normal bacteria present will use the sugar for their growth and as a bi-product use hydrogen. This hydrogen will be absorbed via the gut lining and then it will leave the body in the child’s breath. This can be detected by simply collecting one breath every 30 minutes or so and analysing it for the amount of hydrogen.
It is a perfectly safe test but can induce temporary gastrointestinal symptoms of malabsorption during the testing process.