Lactose Malabsorption Testing in Daily Clinical Practice: A Critical Retrospective Analysis and Comparison of the Hydrogen/Methane Breath Test and Genetic Test (C/T-13910Polymorphism) Results

The aim of this study was to establish a retrospective evaluation and comparison of the hydrogen/methane (H2/CH4) breath test and genetic test (C/T−13910polymorphism) results in lactose malabsorption testing. In total 263 consecutive patients with suspected lactose malabsorption were included in this study. They underwent the H2/CH4breath test following the ingestion of 50 g lactose and were tested for the C/T−13910polymorphism. In total 51 patients (19.4%) had a C/C−13910genotype, indicating primary lactose malabsorption. Only 19 patients (7.2%) also had a positive H2/CH4breath test. All in all 136 patients (51.69%) had a C/T−13910and 76 patients (28.91%) a T/T−13910genotype, indicating lactase persistence. Four patients (1.5%) with the C/T−13910genotype and one patient (0.4%) with the T/T−13910genotype had a positive H2/CH4breath test result, indicating secondary lactose malabsorption. Cohen's Kappa measuring agreement between the two methods was 0.44. Twenty patients (7.6%) with a positive H2/CH4peak within 60 minutes after lactose ingestion were classified as patients with lactose-dependent small intestinal bacterial overgrowth (SIBO). In conclusion, only moderate agreement between the breath test and the genetic test was shown. Secondary lactose malabsorption as well as preanalytical limitations of the combined H2/CH4breath test procedure can cause discrepant results. This trial is registered with K-42-13.