Which test is commonly used to diagnose lactose intolerance?

The hydrogen breath test is a common and effective diagnostic tool for lactose intolerance. This test measures the amount of hydrogen in the breath after the patient consumes a lactose-containing beverage. Normally, lactose is digested in the small intestine, but in individuals who are lactose intolerant, lactose is not properly broken down. This undigested lactose passes into the colon, where it is fermented by bacteria, producing hydrogen. This hydrogen is then absorbed into the bloodstream and eventually exhaled in the breath. An elevated level of hydrogen in the breath indicates that lactose is not being absorbed properly, confirming lactose intolerance.

Other testing methods, while related to gastrointestinal issues, are not as direct in assessing lactose malabsorption. For instance, a blood glucose test checks blood sugar levels and is not specific for lactose intolerance. A stool acid test can be used for lactose intolerance, particularly in infants, by measuring the acidity of stool; however, it is less commonly used in adults. An upper GI series is an imaging study that examines the upper digestive tract but does not provide direct information about lactose digestion, thus making it unsuitable for diagnosing lactose intolerance.