Subjects in the “normal” group had a normal amount of hydrogen, 20 ppm or less, and a normal amount of methane, 3 ppm or less. If subjects had greater amounts than the normal amount of hydrogen (≥20 ppm) detected but had less than the normal amount of methane (≤3 ppm), they were considered hydrogen positive (represented by the “Hydrogen Only” bar), while ≥3 ppm of methane detected but ≤20 ppm of hydrogen was considered methane positive (represented by the “Methane Only” bar). If subjects had greater than the normal amounts of both gases (≥20 ppm of hydrogen and ≥3 ppm), they were considered hydrogen and methane positive (represented by the “Methane and Hydrogen” bar).
