To diagnose lactose intolerance, your doctor will ask about your symptoms, may ask you to drink a glass of milk to see if this triggers them and may take a blood sample after you have drunk some milk to measure your blood sugar level. If the level increases only a little or not at all, this suggests that lactose hasn't been digested and absorbed into your bloodstream-a sign of lactose intolerance. Your doctor may ask you for a stool sample, which will be sent away for testing for acids that are produced by undigested lactose in your bowel, eg lactic acid. Your doctor may ask you to remove dairy products from your diet for a trial period of 3-4wks. No symptoms during this time means you probably have lactose intolerance. You may be referred to a specialist for further tests.
Attribution: BUPA