Diagnosis

Your doctor might suspect lactose intolerance based on your symptoms and your response to reducing the amount of dairy foods in your diet. Your doctor can confirm the diagnosis by conducting one or more of the following tests:

• Hydrogen breath test. After you drink a liquid that contains high levels of lactose, your doctor measures the amount of hydrogen in your breath at regular intervals. Breathing out too much hydrogen indicates that you aren't fully digesting and absorbing lactose.
• Lactose tolerance test. Two hours after drinking a liquid that contains high levels of lactose, you'll undergo blood tests to measure the amount of glucose in your bloodstream. If your glucose level doesn't rise, it means your body isn't properly digesting and absorbing the lactose-filled drink.