There are three common tests done for lactose intolerance, each one has a specific use depending on the patients age and symptoms.  The most common test used is the lactose tolerance test, for most people this is the first test that they will take to diagnose this condition. The other two tests used are the hydrogen breath test and the stool acidity test.

The lactose tolerance test will test your tolerance for ingested lactose by drinking a liquid that contains a large amount of lactose. In healthy people ingested lactose is split into two substances, glucose and galactose which make them absorbable, from there they go from the small intestine to the blood stream. Once the lactose has been ingested during the test, blood tests are taken to measure the blood glucose level. If a person’s body absorbs lactose properly then the blood glucose level will rise after the ingestion of the lactose, but if they are lactose intolerant the blood glucose level will not rise.

A hydrogen breath test can also be used to test for lactose intolerance in adults. Normally there is very little hydrogen in a person’s breath, however an overgrowth of bacteria in the intestine can cause there to be higher amounts of hydrogen. Bacterial overgrowth is what occurs when food does not digest properly or moves too slowly through the intestines.

During a hydrogen breath test your breath will be tested at the beginning of the test and then you will be given something to drink that contains lactose. Your breath will then be tested every fifteen minutes for two hours to see if the presence of hydrogen increases as the lactose solution digests. If there are high levels of hydrogen in your breath it means that the lactose is not digesting properly.

A stool acidity test is the final test that may be used to diagnose lactose intolerance; this test is usually reserved for infants as giving them the large doses of lactose required for the other tests can be dangerous to them.  Also since the other two tests require multiple breath or blood samples this may be difficult to achieve with a very young child. In a stool acidity test the patient is again given lactose albeit a smaller dose, in the lactose intolerant child the lactose will not be completely digested and can result in stools with a much higher acidity.