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Everything you need to know about hydrogen breath tests

Nausea, heartburn, indigestion, upset stomach, diarrhea—this group of gastrointestinal symptoms can cause a lot of distress. And, they’re often mysterious. It can be hard to pinpoint exactly what’s causing all that tummy trouble.

Enter the hydrogen breath test. This simple, non-invasive assessment measures gas levels in your breath to determine exactly why you’re feeling those stomach complications, whether it’s from bacterial overgrowth or just plain indigestion. 

How does a hydrogen breath test work?

Taking a hydrogen breath test is a pretty straightforward process, but it requires preparation. You’ll have a special diet before the test, spend about two hours in the doctor’s office on the day of the test, and then wait about two weeks for your results.

Preparing for the test

Depending on your doctor, preparation can begin anywhere from four weeks to a day before the exam. 

  • A month before, stop taking antibiotics and avoid having a colonoscopy. 
  • Two weeks before, stop taking probiotics. 
  • One week before, cut off laxative usage, smoking, and exercise.
  • Two days before, stop taking any prokinetics. 

Prokinetics are medicines that are generally taken for acid reflux (think Reglan, Pepcid, and Nexium) that work by increasing motility. That means they speed up the time it takes for the contents of your stomach to empty, thereby eliminating whatever might cause the acid reflux—but also eliminating the bacteria the hydrogen test is trying to identify. “We want to know if the patient is having bacterial overgrowth,” says Mackenzie Jarvis, D.M.Sc., an instructor in the department of internal medicine and gastroenterology fellow at Atrium Health Gastroenterology and Hepatology. “These medications can move things faster and leave you without a clear answer.”

One day before, you must follow a strict, “low-residue” diet. It limits foods that are high in fiber, starches, carbs, and sugar. Jarvis says to avoid pasta, fruit, milk, cheese, grainy breads, ice cream, dairy products, and soda. You can still have chicken, fish, eggs, water, coffee, tea, and limited amounts of white bread and white rice (since they are low in fiber). 

The day of the test, don’t eat or drink anything aside from water (that includes breath mints and chewing gum).

During the test

The day of your test, you’ll spend about two hours in the doctor’s office. First, your physician will give you a sugar solution to drink. Jarvis gives her patients a glucose drink, and Mercy Medical Center gastroenterologist Bryan Curtin, M.D., gives his patients either glucose, lactulose, fructose, fructan, or lactose. Glucose is the most typical.

For the first hour after drinking the solution, you’ll blow into a breath collection device every 15 minutes. It looks like a bag with a test tube attached. In the second hour, you’ll blow into the device every 30 minutes. Dr. Curtin asks his patients to keep a diary of how they’re feeling throughout the test, noting if they’re having any symptoms. Meanwhile, lab techs will be analyzing the amount of hydrogen gas and methane gas in each breath sample you give.

“The glucose gets broken down in the small intestine,” Jarvis says. “If there are bad bacteria in the small intestine, it ferments, producing a byproduct of the glucose as hydrogen and methane. We read the study to see if there’s an increase in hydrogen or methane past the baseline. If there’s an increase in one or both, that will determine the treatment.”

Some hospital systems use an at-home testing kit, but because of the equipment used and the very specific collection methods, it’s not common yet. 

After the test

Typically, patients receive their test results in about two weeks. Your doctor will analyze the results to see if and when large amounts of hydrogen or methane appear in your breath samples. Jarvis’ office compiles the results into a graph in order to read them easier compared to the baseline sample. 

According to Dr. Curtin, if there’s a hydrogen or methane increase of 20 parts per million or more, that signifies a problem. He also notes that “if the patient develops diarrhea during the test, the test is positive regardless of gas values.” An increase in symptoms during the test signifies visceral hypersensitivity.

What does a hydrogen breath test diagnose?

A hydrogen breath test is mainly used to diagnose SIBO, or small intestinal bacterial overgrowth. But, it’s also used to detect other digestive disorders such as:

  • Intestinal methanogen overgrowth (IMO)
  • Abnormal digestion of dietary sugars
  • Rapid small bowel transit time

Hydrogen breath tests can help to diagnose irritable bowel syndrome (IBS) by identifying visceral hypersensitivity (or, acute abdominal pain—a symptom of irritable bowel syndrome). They are a tool that can help rule out other conditions that might be causing symptoms that look like IBS. 

A recent study by Imperial College London recently found that hydrogen breath tests can also detect esophageal and gastric cancer in the early stages.


If you’re diagnosed with SIBO, or small intestinal bacterial overgrowth, it means that bacteria from other parts of your gut have started to collect in the small intestine—and they shouldn’t be there. 

Symptoms usually include:

  • Cramping
  • Diarrhea
  • Abdominal bloating or distention
  • Nausea
  • Abdominal fullness or discomfort
  • Foul-smelling gas 

The treatment for SIBO is a round of antibiotics (usually neomycin or augmentin). Even with treatment, though, SIBO can come back, especially in patients with autoimmune diseases—they may get SIBO as much as once a month, Jarvis says.

RELATED: Antibiotics 101


IMO, or intestinal methanogen overgrowth, means that bad bacteria have piled up during a bout of constipation. You’ll have all the same symptoms as SIBO, except with constipation instead of diarrhea. Treatment is similar, too—a round of both general antibiotics and ones specifically for your gut, in addition to treatment for constipation.

RELATED: How gut health impacts your well being

Abnormal digestion of dietary sugars

This diagnosis means that you have trouble digesting sugars or dairy—generally known as fructose intolerance (which includes the sugars found in onions, artichokes, pears, and wheat) or lactose intolerance (the sugar found in milk products). This diagnosis, sometimes called malabsorption, also has similar symptoms to SIBO. 

Unfortunately, these conditions don’t have a cure. Instead, you can manage symptoms by eliminating certain foods from your diet. If you’re lactose intolerant, some over-the-counter enzyme products, like Lactaid, may help as well. Particularly for those with who cannot properly digest lactose, ensure you’re getting enough calcium through supplements.

RELATED: What vitamins should I take?

Rapid small bowel transit time

If you have rapid small bowel transit time, it means food moves through your small intestine at a quicker pace than normal, leading to diarrhea, abdominal pain, bloating, and flatulence. Depending on the underlying reason for your speedy transit time, you may only be able to treat the symptoms. Take antidiarrheals, avoid carbonated drinks, and skip out on foods that may cause excess gas.

How accurate are hydrogen breath tests?

Hydrogen breath testing can sometimes give false positives, and, depending on the substrate used, can be more or less sensitive intended. Plus, some labs use different parameters for when to measure gas levels—like taking breath measurements every 90 minutes for a longer test, or every 30 minutes from the start of the test—which can lead to skewed results. At-home tests have even more room for error in the preparation and administration of the test.

How much does a hydrogen breath test cost?

Costs for hydrogen breath tests vary, depending on both your healthcare provider and your insurance. The cash price can range from $145-$400. Check with your insurance plan to see if the test and any medications you need are covered. Or, talk to your doctor about ways to reduce costs.

Hydrogen breath tests are the most widely used, preferred option for diagnosing SIBO and IMO. A few more expensive, more invasive alternatives exist. One involves an upper endoscopy during which a doctor aspirates fluid from your small intestine. Another uses a capsule that you swallow—it collects fluid that doctors use to then count the number of bacteria in the small intestine. 

If you think you might have SIBO or IMO, contact your healthcare provider to find out if the test is right for you.