What Is the Basic Principle of the Hydrogen Breath Test?
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Hydrogen Breath Test - Principles, Uses, and Types

Published on Jan 30, 2023 and last reviewed on Feb 01, 2023   -  5 min read


The pathophysiology of functional gastrointestinal disorders is extensively investigated using hydrogen breath tests. Read this article to know more.


The hydrogen breath test (HBT) has gained popularity in clinical practice due to its effectiveness in diagnosing small intestinal bacterial overgrowth (SIBO) and carbohydrate intolerance, including the malabsorption of lactose and fructose, which have been suggested to be important for GI disease symptoms. The glucose hydrogen breath test is preferred for SIBO diagnosis, while the lactose and fructose hydrogen breath tests are used to identify the maldigestion of lactose and fructose, respectively. The lactulose hydrogen breath test is also commonly used to determine the oro-cecal transit time for gastrointestinal motility. These methods are non-invasive and low-cost.

Several patients with functional gut disorders are not aware of the link between diet and the gastrointestinal symptoms they are experiencing. Patients with chronic symptoms may consider their condition normal and be unaware that their symptoms can be managed effectively after a proper evaluation. Patients with abdominal pain, bloating, flatulence, and altered bowel movements (diarrhea and constipation) or who have a medical condition of irritable bowel syndrome or celiac disease, might well have underdiagnosed carbohydrate malabsorption, also known as SIBO.

What Is the Basic Principle of the Hydrogen Breath Test?


  • Bacteria in the intestines usually produce hydrogen gas as a byproduct of carbohydrate fermentation. Bacteria can only perform this task in the bowel when dietary carbohydrates are not absorbed in the small intestine and remain undigested as they pass through the digestive tract into the large intestine.

  • Although a portion of the hydrogen gas generated by the bacteria is sent out as flatus or used to make other molecules such as sulfides, acetate, and short-chain fatty acids, the vast majority of the gas is absorbed into the bloodstream through the lining of the large intestine.

  • The gas is subsequently delivered to the lungs through the bloodstream, where gaseous exchange occurs in the lungs and is expelled as expiratory air.

  • Bacterial fermentation in the gut is the only source of hydrogen gas in the breath. The same holds true for methane gas, which is exhaled by some but not all individuals.

  • Methane is produced from hydrogen by bacteria in the large intestine. The amount of hydrogen and methane gases expelled from the lungs may be readily determined by obtaining a breath sample and analyzing it using a piece of breath-testing equipment

What Are the Uses of Hydrogen Breath Testing?

The following three conditions are diagnosed using hydrogen breath testing:

  • The first condition is for evaluating small intestinal bacterial overgrowth (SIBO), a disease in which more colonic bacteria are present than usual in the small intestine.

  • The second condition is the malabsorption of carbohydrates when dietary sugars are not digested. Lactose, the sugar in milk, is the most common sugar that is poorly digested. Lactose-intolerant people are incapable of digesting lactose. Other sugars, such as sucrose, fructose, and sorbitol, may also be tested.

  • The third condition determines whether food moves quickly or slowly through the small intestine.

All the above three conditions can produce gastrointestinal symptoms such as abdominal pain, flatulence, bloating, diarrhea and distention.

How Is the Patient Prepared for a Hydrogen Breath Test?

  • Antibiotics should be stopped for four weeks before the test.

  • Slowly digested foods (such as beans, bran, and high-fiber cereals) should be avoided twenty-four hours before the test, and follow a low-fiber diet.

  • Patients should stop taking fiber supplements and laxatives one day before the test.

  • Patients should stop taking food at least twelve hours before the procedure.

  • Patients are asked not to smoke and sleep two hours before or during the test.

What Are the Types of Hydrogen Breath Tests?

  1. Glucose Hydrogen Breath Test: Glucose is easily absorbed into the small intestine under normal conditions. If there is an overgrowth of bacteria in the (upper) small intestine, bacterial fermentation of glucose and generation of hydrogen can occur before glucose absorption. As a result, a hydrogen breath test exhibits a rise after taking glucose, indicating an excess of bacteria in the small bowel (overgrowth of bacteria is present in the intestines). SIBO is an increase of hydrogen greater than ten parts per million above the baseline value in two subsequent measurements.

  2. Lactose Hydrogen Breath Test: This test is used to measure whether or not an individual has a problem digesting lactose products (for example - milk, cheese, and ice cream). Symptoms of lactose intolerance (LI) include diarrhea, flatulence, abdominal cramps, and bloating. LI occurs when lactose is not hydrolyzed to galactose and glucose due to a lactase deficiency or absence of the enzyme. SIBO is generally defined as a rise of hydrogen greater than twenty parts per million above the baseline value in two subsequent readings.

  3. Fructose Hydrogen Breath Test: This test determines if the patient has difficulties digesting fructose. Fructose is the natural sugar in honey, vegetables, fruits, and grains. It is a single molecule of sugar that many people do not effectively absorb. Malabsorption of fructose is a digestive disorder in which appropriate fructose absorption does not occur in the small intestine. This poorly absorbed fructose travels to the large bowel, where it becomes fermented by the intestinal flora. Bacterial fermentation creates gas and other gastrointestinal (GI) symptoms.

  4. Sorbitol Hydrogen Breath Test: Sorbitol is an alcohol of sugar (polyol) that is frequently used as a sweetener in sugar-free sweets and chewing gum, as well as diet and diabetic foods. It is generated by the human body, is present in fruits, beer, and berries, and is also found in some medicines (such as mouthwashes, cough syrups, and laxatives) and cosmetics. Sorbitol contains low calories and is less likely to create dental caries than sucrose (table sugar). The small intestine absorbs glucose passively and much slower than other sugars. This permits moderate doses to be malabsorbed and fermented in the colon, particularly in individuals with rapid intestinal transit. At doses of five grams or higher, many healthy people experience abdominal bloating, gas, cramps, and diarrhea.

  5. Lactulose Hydrogen Breath Test: Lactulose is a galactose and fructose disaccharide compound. Due to the lack of naturally occurring enzymes, lactulose is carried intact to the colon and fermented by colonic bacteria. Hydrogen is one of the byproducts of metabolism. The time between ingesting lactulose and experiencing an increase in breath hydrogen over baseline is calculated.


Breath evaluation as a clinical assessment has several advantages. It provides quick and accurate results, allowing physicians to diagnose and treat patients more effectively and quickly. The procedure is non-invasive and relatively simple and painless to obtain the sample; the sample contains high information (a single breath test can be used to evaluate many abnormalities or disease markers), it is cost-effective to the patient, and it affords itself simple administration. Furthermore, analyzing breath after ingestion of a substrate can help diagnose SIBO, carbohydrate malabsorption, and OCTT.

Last reviewed at:
01 Feb 2023  -  5 min read




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