Serum diamine oxidase activity is associated with lactose malabsorption phenotypic variation

•Lactose breath testing and serum diamine oxidase (DAO) measurements are performed.•Association with lactose malabsorption phenotypic variation is investigated.•Serum DAO activity level < 10 U/mL associates with higher exhaled H2 levels.•Lactose malabsorbers with low DAO activity (< 10 U/mL) tend to report symptoms more often.

ObjectivesRecently, an intermediate lactose intolerance (LI) phenotype based on the lactase gene (LCT) C/T-13910 polymorphism was proposed. However, a multifactorial genesis of LI phenotypic variation including endogenous and exogenous factors cannot be ruled out. Therefore, this study was conducted to investigate a possible association between serum diamine oxidase (DAO) and LI phenotypes in individuals with lactose malabsorption (LM).Design and methodsA total of 121 ambulatory patients with LM were included in this retrospective study. The lactose hydrogen breath test (LHBT) and serum DAO activity measurements were performed on the same day. A thorough anamnesis with respect to gastrointestinal symptoms was carried out at the initial consultation.ResultsIn total, 44 (36.4%) patients with a serum DAO activity < 10 U/mL showed higher H2 levels after 60 (mean: 53.7 ± 57.6 vs 34.5 ± 31.7 parts per million [ppm], p = 0.116), 90 (mean: 70.3 ± 57.5 vs 52.7 ± 41.4 ppm, p = 0.184) and 120 min (mean: 98.9 ± 72.5 vs 67.9 ± 44.9 ppm, p = 0.012) during LHBT compared to 77 (63.6%) patients with a serum DAO activity ≥ 10 U/mL. Individuals with a serum DAO activity < 10 U/mL tended to report gastrointestinal symptoms during the LHBT more often (p = 0.091).ConclusionsOur findings suggest that patients with LM and a serum DAO activity level < 10 U/mL had higher end-expiratory H2 levels and tended to be more symptomatic during the LHBT compared to LM patients with DAO activity levels ≥ 10 U/mL.