H2 exhalation functional test

What is the Hydrogen Breath Test (H₂ Breath Test)?

The hydrogen breath test is a non-invasive gastroenterological examination that helps diagnose certain digestive conditions by measuring changes in the amount of hydrogen gas in the air exhaled by the patient. The test is based on the principle that hydrogen gas (H₂) in the body is only produced when intestinal bacteria ferment carbohydrates.

Hydrogen Breath Test with Lactose

This version of the test is used to detect lactose intolerance.
Lactose (milk sugar) is a disaccharide made up of glucose and galactose, and it needs an enzyme called lactase to be broken down in the small intestine. Only in this split form can it be absorbed. If someone lacks sufficient lactase, the lactose is not digested and passes into the colon, where bacteria break it down, producing hydrogen gas. This hydrogen enters the bloodstream, travels to the lungs, and is exhaled—where it is detected by the test device.

A positive result is sufficient to diagnose lactose intolerance.

Hydrogen Breath Test with Lactulose

This version of the test is used to:

• Measure the small bowel transit time (or orocecal transit time),
• Detect Small Intestinal Bacterial Overgrowth (SIBO).

Lactulose is a synthetic disaccharide that cannot be digested by the enzymes in the small intestine. It reaches the colon unchanged, where it is fermented by bacteria, producing short-chain fatty acids (such as lactic acid and acetic acid), methane, and hydrogen gas.

The transit time is determined by identifying the time at which the exhaled hydrogen concentration increases above 20 ppm.
A normal transit time averages around 120 minutes and is determined by comparison to healthy control subjects.
If a glucose or lactose hydrogen breath test shows abnormally early hydrogen production, this suggests SIBO. If the result is normal, the test is used only to determine transit time.

For accurate diagnosis and differentiation between lactose intolerance and SIBO, it is recommended to perform both the lactose and lactulose breath tests on separate occasions.

Hydrogen Breath Test with Fructose

This test is used to detect fructose malabsorption, which is often mistakenly referred to as "fructose intolerance" (hereditary fructose intolerance is much rarer).
Fructose malabsorption occurs when fructose is not absorbed in the small intestine due to temporary or chronic causes. As a result, it reaches the colon, where it is fermented by bacteria, producing acids and gases. This leads to symptoms such as bloating, abdominal pain, diarrhea, fatigue, poor general well-being, headaches, cramps, and loose stools.

These symptoms are often mistaken for Irritable Bowel Syndrome (IBS). The main treatment is a fructose-free diet, and this type of malabsorption can be effectively managed this way.

How the Hydrogen Breath Test is Performed

• Upon arrival, the patient rinses their mouth and throat with an antibacterial solution.
• The first breath sample is taken to establish a baseline hydrogen level.
• If the baseline level is over 10 ppm, the doctor may recommend rescheduling the test.
• The patient drinks a test solution (25–50 grams of lactose or fructose, or 20 grams of lactulose dissolved in 2.5–3 dl of water).
• The patient then breathes into the device at set intervals (every 15–20 minutes) for about 120 minutes.
• The results are immediately available for interpretation.
• The test also monitors any symptoms (nausea, vomiting, bloating, diarrhea) experienced during the procedure.

Preparation is Crucial for Accurate Results

To ensure reliable results, it is essential to strictly follow the preparation guidelines below:

Important Restrictions Before the Test

• You cannot undergo the test if you have a fever or upper respiratory infection.
• Do not take the following before the test:
• Antibiotics or probiotics within 2 weeks
• Acid blockers (PPIs) within 1 week
• Laxatives within 2–3 days
• Dietary Restrictions the Day Before the Test
• From the morning of the day before the test, avoid eating or drinking:
• All vegetables and fruits (raw, cooked, steamed, or in stews or side dishes)
• Legumes (beans, lentils, peas) and gas-producing vegetables (cabbage, broccoli, cauliflower, kale, Brussels sprouts)
• Any foods that contain cooked vegetables or fruits (e.g., soup broth, stew sauces, compote juice)
• Dairy products, milk, cold cuts, or baked goods that contain lactose
• Chocolate, nuts, high-fat foods
• Carbonated drinks, fruit juice, and alcohol
• Do not smoke
• You may eat:
• Cooked, steamed, or plain roasted chicken, turkey, or fish
• Plain boiled rice, pasta, or potatoes (no spices or seasonings)
• Lactose-free cold cuts (look for “lactose-free” labels or the crossed-out milk bottle symbol)
• Lactose-free dairy products
• Lactose-free bread (only water rolls are guaranteed to be dairy-free; always check packaging or allergen labels)
• Still mineral water
• Do not eat after 7:00 PM and do not drink after 9:00 PM on the day before the test.
• Brush your teeth thoroughly that evening.

On the Morning of the Test

• Do not use toothpaste or mouthwash
• Women: avoid lipstick or lip gloss
• Men: do not apply aftershave near the mouth
• No chewing gum, mints, or candy
• Do not take any morning medications
• Do not smoke
• After waking, brush your teeth thoroughly without toothpaste, and do not swallow the rinsing water.
• Repeating this brushing right before leaving for the test is recommended.