2.5. Breath Test

The breath test had been performed for the cases for diagnostic purposes, as previously reported [26]. In detail, the subjects received an oral load of 1 g of lactose/kg of body weight, up to a maximum of 50 g, dissolved in a water solution. One breath sample was taken before the oral lactose load and every 30 min thereafter for a 3 h period. Hydrogen and methane concentrations were measured in parts per million (ppm) by means of a MicroLyzer gas chromatograph (Model DP, Quintron Instruments, Milwaukee, WI, USA) with a solid-state sensor detector (sensitivity 1 ppm, accuracy 2 ppm, linear range 2–150 ppm). The test was judged to be positive when the peak of hydrogen or methane exceeded 20 ppm over the baseline value.