What are the recommended diagnostic tests for confirming lactose intolerance in adults?

The recommended diagnostic tests for confirming lactose intolerance in adults primarily include the hydrogen breath test and lactose tolerance test. The hydrogen breath test is considered the preferred non-invasive diagnostic tool, measuring hydrogen in the breath after ingestion of a lactose load; an increase indicates lactose malabsorption due to bacterial fermentation of unabsorbed lactose in the colon NICE CKS. The lactose tolerance test involves measuring blood glucose levels after lactose ingestion; a failure to rise suggests lactose malabsorption NICE CKS. Additionally, genetic testing for lactase persistence/non-persistence alleles can support diagnosis but is less commonly used in routine clinical practice Misselwitz et al. 2019. Symptom assessment following lactose ingestion is also important but not sufficient alone for diagnosis. Recent European guidelines emphasize the hydrogen and methane breath tests as the most reliable and clinically impactful diagnostic methods for lactose intolerance in adults Hammer et al. 2022. Other tests such as stool acidity tests are less commonly used and have lower diagnostic accuracy. Overall, the hydrogen breath test remains the gold standard in UK clinical practice, supported by both NICE-aligned guidance and recent literature Fassio et al. 2018Misselwitz et al. 2019Hammer et al. 2022.