Lactose Intolerance - Hydrogen Breath Test

Lactose is the sugar found in milk. Lactase is the enzyme in the small intestine that breaks down lactose. The body's ability to make lactase is sometimes lost in a genetically pre-programmed event that usually occurs after childhood. Genetic lactase deficiency is more common in certain ethnic groups, affecting people of Native American, African American, Asian, Mediterranean, and Jewish descent. The body's ability to make lactase may also temporarily be lost following an episode of infectious gastroenteritis (vomiting and diarrhea).

Lactase deficiency causes a build up of lactose in the intestines, which triggers fluid shifts and diarrhea. Because there is not enough lactase to break down the lactose, the lactose is broken down by bacterial fermentation. This fermentation process results in a release of hydrogen gas, which causes cramping and bloating. The hydrogen gas is absorbed by the colon and exhaled by the lungs. The hydrogen breath test for lactose intolerance measures the hydrogen exhaled at various time intervals following the ingestion of a concentrated lactose sugar solution.

Hydrogen Breath Test

The hydrogen breath test typically takes three hours or less and the child and his or her family will know the result of the breath test immediately.

• To achieve accurate baseline values, the study must be performed after a period of fasting (usually eight hours).


• The child is first asked to breathe into the HBT Sleuth machine (which measures the hydrogen levels) to obtain a baseline level of hydrogen (in parts per million or PPM).


• The child then drinks a lactose sugar solution (between 25 and 50 GM, depending on weight) dissolved in water.


• The child then breathes into the machine every 30 minutes for up to 3 hours.


• A rise greater than 20 PPM hydrogen within these 3 hours is diagnostic of lactose intolerance.