Measurement of breath hydrogen and methane, together with lactase genotype, defines the current best practice for investigation of lactose sensitivity.

BACKGROUND: Currently, there is no 'gold standard' for detecting patients with sensitivity to lactose. Biochemical investigation by a breath hydrogen test alone detects <50% cases. Breath methane and symptoms are not recorded as standard practice. The clinical value of analysing C/T(13910) and G/A(22018) polymorphisms, strongly associated with lactose sensitivity, has not been established.

METHODS: Two hundred and ten patients with unexplained gut and systemic symptoms and controls were challenged with 50 g lactose. Breath hydrogen and methane were measured and symptoms recorded. All were genotyped for two polymorphisms, C/T(13910) and G/A(22018).

RESULTS: CC(13910)/GG(22018) in 14.5%, CT(13910)/GA(22018) in 39% and TT(13910)/AA(22018) in 46.5%. One hundred percent of CC(13910)/GG(22018) were lactose sensitive having a breath hydrogen >20 ppm within 6 h and symptoms. But the breath hydrogen test lacked sensitivity and specificity in the other groups. There was elevated breath hydrogen in 21% of CT(13910)/GA(22018) and 15% of TT(13910)/AA(22018) by 6 h, whereas 17 and 30.9% had elevated breath methane alone. Breath methane and breath hydrogen with clinical symptoms improved sensitivity and specificity, increasing detection of lactose sensitivity in genotypes CT/GA and TT/AA from <50 to >75%.

CONCLUSIONS: The data presented define the current best practice for the clinical identification of lactose sensitivity. Patients were first genotyped. Those identified as CC with symptoms should immediately undertake a 12-week lactose-free diet. Those identified as CT or TT should undertake a breath hydrogen and methane test. Those positive for hydrogen or methane along with symptoms or with symptoms only, should also undertake a lactose-free diet. Those with high hydrogen without symptoms should be investigated for causes other than lactose sensitivity.