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, lactose tolerance blood test, and, less commonly, genetic testing. The hydrogen breath test is considered the most practical and widely used method; it measures hydrogen in the breath after ingestion of a lactose load, indicating malabsorption when elevated hydrogen levels are detected due to bacterial fermentation of unabsorbed lactose in the colon ¹.

The lactose tolerance blood test involves measuring blood glucose levels after lactose ingestion; a failure to rise indicates poor lactose digestion ¹. Genetic testing for lactase persistence/non-persistence can be used to identify primary lactase deficiency but does not confirm symptomatic intolerance and is less commonly employed in routine clinical practice (Misselwitz et al., 2019).

Recent European guidelines emphasize the hydrogen and methane breath tests as the preferred diagnostic tools due to their non-invasive nature and good sensitivity and specificity (Hammer et al., 2022). These breath tests can also differentiate lactose malabsorption from other causes of symptoms, such as small intestinal bacterial overgrowth.

In clinical practice, diagnosis often begins with a clinical history and symptom assessment, followed by breath testing to confirm lactose malabsorption and correlate symptoms, as symptoms alone are insufficient for diagnosis ¹ (Fassio et al., 2018).