title: Measurement of breath hydrogen and methane, together with lactase genotype, defines the current best practice for investigation of lactose sensitivity.
abstract: 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.
authors.affiliation: Department of Medical Biochemistry and Immunology, Llandough Hospital, Cardiff and Vale NHS Trust, Llandough, Vale of Glamorgan, South Wales, Cardiff, UK.
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Waud
authors.forename: Stephanie B
authors.initials: SB
authors.lastname: Matthews
authors.forename: Anthony K
authors.initials: AK
authors.lastname: Campbell
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001944:Breath Tests; D002648:Child; D002675:Child, Preschool; D005260:Female; D005838:Genotype; D006801:Humans; D006859:Hydrogen / Q000032:analysis* / Q000378:metabolism*; D043322:Lactase / Q000235:genetics* / Q000378:metabolism; D007787:Lactose Intolerance / Q000175:diagnosis / Q000378:metabolism; D007789:Lactose Tolerance Test / Q000379:methods*; D008297:Male; D008697:Methane / Q000032:analysis* / Q000378:metabolism*; D008875:Middle Aged; D011110:Polymorphism, Genetic / Q000235:genetics; D012680:Sensitivity and Specificity
chemical_list: D006859:Hydrogen; D043322:Lactase; D008697:Methane