Accuracy of lactase gene C/T-13910 polymorphism and hydrogen breath test in a gastroenterology outpatient clinic: a retrospective study

Introduction: Adult type hypolactasia is the most prevalent carbohydrate malabsorption. Aim: To assess the distribution of lactase gene C/T-13910 polymorphism and the accuracy and concordance of a genetic test and H-2 breath test in the diagnosis of adult type hypolactasia. Method: 496 patients with symptoms of lactose intolerance were enrolled in a retrospective study who underwent genetic test using TaqMan polymerase chain reaction and H-2 breath test. Results: The prevalence of C/T-13910 genotypes was: CC 48.1%, TC: 40.5%, and TT: 11.4%. When the genetic test was taken as reference, the sensitivity of the breath test was 84.3%, with a specificity of 95.7%, a positive predictive value of 96.7% and negative predictive value of 80.4%. Conversely, the accuracy of genetic test was: sensitivity 96.6%, specificity 80.4%, positive predictive value 84.3% and negative predictive value 95.7%. The concordance value between the two tests (kappa index) was 0.78. The results were discordant in 11.1% of the cases. Conclusions: In symptomatic patients, the lactase non-persistence genotype CC occurred in almost half of the patients. Both the genetic and the breath tests are sufficiently accurate, with good predictive value and they can be used to set up the diagnosis. Discordant results should be carefully interpreted.