This procedure is used to determine how well the body can digest lactose, the predominant sugar found in milk. After a period of fasting, the patient is given a liquid containing lactose. After ingestion of the liquid, samples of the patients blood glucose (sugar) level are taken over a 2 hour period. The body's digestive enzyme, lactase, breaks lactose down into glucose, which is then absorbed into the blood. If the patients blood glucose level does not rise during this test, then lactose is not being digested properly, resulting in a diagnosis of lactose intolerance. Consult your physician if these apply.