What is the best way to diagnose lactose intolerance?

For most patients, a careful history and a 2-week lactose-free diet that results in resolution of symptoms-which then recur when lactose is reintroduced-is sufficient to make the diagnosis. Other tests may be used for atypical or complicated cases or when the diagnosis of lactase deficiency needs to be confirmed; of these, the hydrogen breath test is the most widely applicable. (SOR C, based on expert opinion.).