title: Comparison of a real-time polymerase chain reaction assay for lactase genetic polymorphism with standard indirect tests for lactose maldigestion.
abstract: OBJECTIVE
  There is a discrepancy in outcome between the lactose tolerance and breath hydrogen tests for lactose maldigestion. The availability of a validated genetic test for lactase polymorphism allows a reevaluation of these tests.
  
  
  METHODS
  Thirty healthy adults participated in a 50-g lactose challenge test at a university clinic. Blood was drawn for genetic and timed blood glucose testing (2 hours), and breath hydrogen was measured (4.5 hours). Lactase genetic polymorphism was assessed by a real-time polymerase chain reaction assay. Participants completed a diet questionnaire, and symptoms were recorded during the lactose challenge. Sensitivity and specificity were calculated for each indirect test. The 2-way kappa coefficient between these tests was evaluated. Student t test and Wilcoxon rank sum test were used to compare variables.
  
  
  RESULTS
  The lactose tolerance test as a standard had an 87.5% sensitivity and 92.7% specificity for genetic status. Only a moderate agreement between lactose tolerance test and breath hydrogen test was observed (2-way kappa coefficient, .53; 95% confidence interval, .22-.83). When genetic status was used as standard, symptoms had a moderate sensitivity and specificity. Lactose tolerance test had very good sensitivity, and the breath test had excellent specificity.
  
  
  CONCLUSIONS
  Both indirect tests independently have good to very good sensitivities and specificities for genetic lactase status. The noted disagreement likely reflects variables that affect the tests independently of intestinal lactase status. The value of these tests in the light of the availability of genetic testing is discussed.
authors.affiliation: Division of Gastroenterology, Sir Mortimer B. Davis Jewish General Hospital, Montreal, Quebec, Canada. aszilagy@gas.jgh.mcgill.ca
authors.forename: Andrew
authors.initials: A
authors.lastname: Szilagyi
authors.forename: Paula
authors.initials: P
authors.lastname: Malolepszy
authors.forename: Elise
authors.initials: E
authors.lastname: Hamard
authors.forename: Xiaoqing
authors.initials: X
authors.lastname: Xue
authors.forename: Nir
authors.initials: N
authors.lastname: Hilzenrat
authors.forename: Mary
authors.initials: M
authors.lastname: Ponniah
authors.forename: Elizabeth
authors.initials: E
authors.lastname: MacNamara
authors.forename: George
authors.initials: G
authors.lastname: Chong
mesh_terms: D000328:Adult; D001944:Breath Tests; D005260:Female; D006801:Humans; D006859:Hydrogen; D043322:Lactase / Q000235:genetics*; D007787:Lactose Intolerance / Q000175:diagnosis* / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic
chemical_list: D006859:Hydrogen; D043322:Lactase