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.

Haptoglobin is a protein that your liver produces. It combines with hemoglobin, which transports oxygen to your organs and tissues via the red blood cells.  The haptoglobin test is a test for hemolytic anemia.

Hepatitis B surface antigen (HBsAg) is a distinctive serological marker of acute or chronic hepatitis B infection. HBsAg is the first antigen to appear following infection with HBV and is generally detected 1-10 weeks after the onset of clinical symptoms. HBsAg assays are routinely used to diagnose suspected HBV infection and monitor the status of infected individuals to determine whether the infection has resolved or the patient has become a chronic carrier of the virus.

The HCO3- - Arterial marker on Labcorp's Arterial Blood Gas (ABG) Panel measures the concentration of bicarbonate ions (HCO3-) in the arterial blood. Bicarbonate plays a crucial role in maintaining the acid-base balance of the body, functioning as a buffer to regulate the pH of blood. It helps neutralize excess acids or bases, thus stabilizing the body’s pH levels. HCO3- is closely linked with the respiratory system's ability to excrete CO2 and the kidneys' ability to excrete or retain bicarbonate, making it a key indicator of both metabolic and respiratory health.