title: Carbohydrate challenge tests:  do you need to measure methane?
abstract: OBJECTIVE
  Breath tests that measure hydrogen (H2) have been judged reliable for the detection of lactose maldigestion (LM) and fructose malabsorption (FM). Recently, methane (CH4) testing has been advocated and measurement of CH4 in addition to H2 has been shown to increase the diagnostic accuracy for LM.
  
  
  OBJECTIVE
  This study was designed to consider the additional yield from CH4 measurement in patients tested for LM and FM.
  
  
  METHODS
  Patients reported for testing after an overnight fast, not smoking and with their prior evening meal carbohydrate restricted. After challenge with 50 g lactose or 25 g fructose in water, end-alveolar breath samples collected over a 4-hour duration were analyzed for H2 and CH4. Diagnostic positivity was compared using a cutoff level of 20 ppm increase above fasting baseline for H2 alone, which is consistent with consensus guidelines, versus H2 plus twice CH4, which recognizes that CH4 consumes twice the hydrogen.
  
  
  RESULTS
  There were 406 LM performed in 93 men and 313 women. Of those tested, 124 (30%) had a positive test for H2 and 139 (34%) had a positive test for H2 + CH4 ×2. There were 178 FM tests performed in 31 men and 147 women. Of those tested, 17 (9%) had a positive test for H2 and 42 (23%) had a positive test for H2 + CH4 ×2.
  
  
  CONCLUSIONS
  If H2 alone was measured without additional CH4 analysis, 4% of patients with LM and 14% patients with FM would not have been identified.
authors.affiliation: From the Division of Gastroenterology, University of South Alabama College of Medicine, Mobile, Alabama 36693, USA.
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Knudsen
authors.forename: Jack A
authors.initials: JA
authors.lastname: Di Palma
mesh_terms: D001944:Breath Tests / Q000379:methods*; D050260:Carbohydrate Metabolism; D005260:Female; D006801:Humans; D006859:Hydrogen / Q000032:analysis*; D007787:Lactose Intolerance / Q000175:diagnosis*; D008286:Malabsorption Syndromes / Q000175:diagnosis*; D008297:Male; D008697:Methane / Q000032:analysis*; D012189:Retrospective Studies
chemical_list: D006859:Hydrogen; D008697:Methane