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 NICE CKS.
The lactose tolerance blood test involves measuring blood glucose levels after lactose ingestion; a failure to rise indicates poor lactose digestion NICE CKS. 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 NICE CKS Fassio et al. 2018.
Key References
- CKS - Cow's milk allergy in children
- CG61 - Irritable bowel syndrome in adults: diagnosis and management
- CKS - Dyspepsia - unidentified cause
- (Fassio et al., 2018): Lactose Maldigestion, Malabsorption, and Intolerance: A Comprehensive Review with a Focus on Current Management and Future Perspectives.
- (Misselwitz et al., 2019): Update on lactose malabsorption and intolerance: pathogenesis, diagnosis and clinical management.
- (Hammer et al., 2022): European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.