Hydrogen is produced when certain bacteria in the small intestine consume sugars and produce hydrogen gas as a byproduct.

Hydrogen levels are considered abnormal when they rise greater than ≥20 ppm (parts per million) from the baseline within 90 minutes.

In healthy humans, hydrogen gas is exclusively produced by intestinal bacteria - primarily a result of carbohydrate fermentation by anaerobic bacteria in the colon. In SIBO, fermentation of the malabsorbed lactulose substrate by bacteria residing in the small intestine results in elevated concentration of exhaled hydrogen (H2).

Trio-smart measures a third fermented gas, hydrogen sulfide (H2S). Which is produced by sulfate-reducing bacteria utilizing H2 to produce H2S. Clinical trials have noted that H2S is associated with diarrhea in patients. In a 2021 study, it was found that healthy subjects had H2S levels of <3.00 ppm. Levels of hydrogen sulfide ≥3.00 ppm are associated with diarrhea and indicative of excess hydrogen sulfide. Higher levels of hydrogen sulfide predict more severe diarrhea.

Hemoglobin (Hb) is the iron-containing oxygen transportation protein in red blood cells. It's rate of binding oxygen depends on the number oxygen molecules already bound.

Hafnia alvei plays an active role in fermented foods, such as cheeses, kimchi and other traditional fermented dishes. Increased serum IgA and IgM have been found in chronic fatigue patients with increased intestinal permeability to Hafnia alvei, Pseudomonas aeruginosa, Morganella morganii, Proteus mirabilis, Pseudomonas putida, Citrobacter koseri, and Klebsiella pneumoniae. Hafnia alvei has the potential to decarboxylate histidine to histamine.