The lactose tolerance test is a test which is used to diagnose an inability to digest lactose – the sugar in milk.
Normally, lactose is digested in the intestine by an enzyme into two smaller sugars – galactose and glucose which are the absorbed into the body. People with lactose intolerance have a lack of the intestinal enzyme so the lactose is not absorbed in the small intestine and it is used by the bacteria in the colon to produce chemicals that cause diarrhea, gas and abdominal pain.
During lactose tolerance test, a person drinks a liquid that contains lactose. After a period of two hours, several blood samples are taken to measure the blood glucose level and it rises in the blood due to the absorption of glucose. The lactose tolerance is normal and does not rise if there is lactose intolerance.
Other tests like hydrogen breath test and stool acidity test can be included to detect lactose intolerance. Stool acidity test is primarily used in infants and very young children.
People who have lactose intolerance must not drink regular cow’s milk, so they must substitute it with rice or soy milk or special cow’s milk with an enzyme that digests the lactose so that the smaller sugars can be absorbed in the small intestine.