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SIBO is often misdiagnosed or under-diagnosed, according to a 2013 study published in Therapeutic Advances in Chronic Disease. (Sachdev, 2013)

One of the challenges in diagnosing SIBO is the fact that many of the symptoms of SIBO — such as bloating, diarrhea, gas, abdominal pain, and weight loss — are similar to those of irritable bowel syndrome (IBS).

To complicate matters further, SIBO is often a cause of IBS itself.

There are currently four tests available that can either directly assess for SIBO or can indicate its presence. Consider taking one or a combination of them. We discuss each one below.

Who Should Get Tested for SIBO?

Diagnosing SIBO by symptoms alone is impossible. Testing to rule out or diagnose SIBO is crucial if you have chronic digestive symptoms without a conclusive diagnosis.

If you experienced chronic gut symptoms and were tested with a colonoscopy, ultrasound, CT scan, or gastroscopy and these traditional tests have failed to provide a conclusive diagnosis, then testing for SIBO may be your best next step.

Types of SIBO Tests

Every SIBO test has its benefits and drawbacks. We detail each below and make recommendations on specific tests you can take.

Breath Tests

Although breath tests are not considered to be the gold standard for testing for SIBO — a small bowel aspiration is — they are the most accessible and affordable tests.

Archaea and bacteria are the sole sources of methane, hydrogen, and hydrogen sulfide gases in the gut by fermenting certain carbohydrates.

In a healthy individual, these gases are produced in decent amounts in the large intestine (colon) only. In people who suffer from SIBO, archaea and bacteria are also present in the small intestine in large numbers where they also produce these gases.

These gases are largely responsible for the various symptoms typical of SIBO.

A SIBO breath test is used to measure the amounts of methane and hydrogen produced in the intestines. The test measures for these gases after you ingest sugar that comes with the test.

The measurement of these two gases can indicate if SIBO exists in the small intestine. Excessive production of methane indicates an overgrowth of archaea — an example being Methanobrevibacter smithii). High levels of hydrogen indicate bacterial overgrowth.

If you experience SIBO symptoms yet receive a “normal” result from this test, this may indicate an overgrowth of hydrogen sulfide producing bacteria or another cause of the IBS. No commercially available test measures hydrogen sulfide, although this is expected to change later in 2019.

You must fast for 12 hours before this test. You may drink water, and you should take your prescription medication, but no food is allowed.

For the 12 hours preceding your fast, you must follow a specific diet. Constipated people must follow this diet for 48 hours. The details of this diet sometimes vary depending on the lab, but it’s best to follow the strictest version — detailed below.

The purpose of this is to eliminate your exposure to fermentable carbohydrates, such as wheat, onions, and fruit, to prevent a false positive test result. The only foods allowed in the SIBO test diet are:

  • Broiled or baked chicken or turkey
  • Broiled or baked fish
  • Plain steamed white rice
  • Clear broth (no bones or vegetables)
  • Eggs
  • Tofu
  • Minimal olive oil or coconut oil for cooking
  • Hard cheeses such as parmesan and pecorino, unless there is a dairy allergy or intolerance

Permitted beverages include plain non-carbonated water, and weak coffee and tea with no cream, sugar or artificial sweetener. Avoid herbal teas.

Once you have completed your 12-hour or 48-hour fast, you will be asked to breathe into a tube. This will measure your baseline levels of methane and hydrogen. You will then be asked to drink a solution of glucose or lactulose (carbohydrates) and take breath samples every 20 minutes for three hours.

Although some laboratories offer one and two-hour tests, a three-hour test is considered to be preferable because every person experiences different transit times. It’s also useful to see the pattern of gas production for both the small and large intestines.

The usual cut-off mark between the small intestine and large intestine is 100 minutes. Results after the 100-minute mark do not usually reflect what is occurring in the small intestine. Levels measured between 100-120 minutes are considered borderline.

Currently, SIBO breath tests are not standardized. Choose a test that offers the following:

  • Measurement of both methane and hydrogen
  • Measurement of carbon dioxide to ensure the test samples are valid
  • Measurement of gas levels at every 20-minute point
  • Grams of test sugars — ideally 10g lactulose, 75g glucose (1g/kg body weight), 25g fructose
  • 3hr test duration

Many medical experts have conflicting views about whether glucose or lactulose is the best carbohydrate solution to use for the SIBO test. It is best to have both tests done along with fructose if possible (see below).

Glucose tends to detect SIBO cases where the bacteria are located higher up in the small intestine — it can miss cases of SIBO located further down the digestive tract.

Not all bacterial species present in SIBO can ferment the lactulose, meaning some cases may be missed.

Other sugars such as lactose and fructose testing are more appropriate for detection of malabsorption rather than for SIBO, although SIBO can itself be a cause of fructose malabsorption.

A 2014 study, published in the Indian Journal of Clinical Biochemistry, showed that a glucose hydrogen breath test is more suitable for SIBO diagnosis, whereas a lactose breath test is more suitable for the diagnosis of lactose maldigestion. (Rana, 2014)

Another concern about the use of lactulose in SIBO testing was highlighted in a 2014 paper, published in Digestion. In a comparison study of glucose and lactulose breath tests for the diagnosis of SIBO, glucose was shown to be more reliable and less prone to false positive results. (Ghoshal, 2014)

The breath test is largely considered to be the easiest and most accessible way to test for SIBO. It is non-invasive, convenient, and affordable. You can purchase a SIBO test kit so you can do the test at home.

However, SIBO breath testing is not without its limitations. For example, SIBO breath testing currently does not measure hydrogen sulfide as mentioned above.

Hydrogen sulfide is a third gas which may be present in SIBO. However, less research has been conducted on this type of bacterial overgrowth compared to the other gases in terms of causes and treatment.

Finally, since there is no standardized breath test for SIBO, you may get a positive diagnosis from one practitioner, and a negative diagnosis from a different practitioner depending on the interpretation of results.  

We recommend ordering lactulose, glucose, and fructose for the most accurate assessment.

Recommended Breath Test Labs

Small Bowel Aspirate Test

Before the advent of the breath test discussed above, the small bowel aspirate was the test of choice.

This test requires a sample of fluid from the small intestine. The sample is collected using a procedure known as esophagogastroduodenoscopy (EGD).

For the test, your doctor places a tube into your nose. The tube passes down through your stomach until it reaches your small intestine. Once it is in place, a small sample of fluid is removed. The fluid is tested in a laboratory to analyze which types of bacteria are present.

This test is quite invasive; its effectiveness has also been questioned. In a 2013 study published in Alimentary Pharmacology and Therapeutics, a review of medical literature on SIBO testing indicated that the small bowel aspirate test might not be adequate at measuring the overall growth of SIBO in the small intestine. (Grace, 2013)

Furthermore, some of the species of bacteria that grow in the small intestine cannot be cultured effectively. This is one reason why the small bowel aspirate test is not as commonly used to diagnose SIBO as it used to be.

This test is available through gastroenterologists.

Stool Tests

A SIBO stool test can show some signs of SIBO, such as changes in bacterial composition and fat malabsorption. Stool testing can also be used to rule out other causes of chronic digestive disorders, such as parasites.

A stool test can also measure levels of yeast and inflammation in the large intestine (colon).  

However, stool testing for SIBO is not without its problems. This is mainly due to the different environments in the small and large intestine.

Although a stool test can provide relevant information about the current state of the digestive tract, it may not be an accurate test for SIBO diagnosis.

Recommended labs

Urine Organic Acids Testing

Urine organic acids testing can reveal signs of bacterial or yeast overgrowth. However, due this test is unable to show the specific location of the bacterial overgrowth, on its own. As a result, it is not considered to be a reliable test for diagnosing SIBO.

Recommended labs

Of the four available tests for assessing SIBO, the breath test is currently the best choice. However, there are drawbacks to each test — including the breath test. Consulting with an experienced healthcare provider trained in SIBO diagnosis and treatment is ideal.

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Research Citations

  • Sachdev AH, Pimentel M. Gastrointestinal bacterial overgrowth: pathogenesis and clinical significance. Therapeutic advances in chronic disease.  2013 Sep; 4(5): 223–231. doi: 10.1177/2040622313496126.
  • Saad RJ, Chey WD. Breath testing for small intestinal bacterial overgrowth: maximizing test accuracy. Clinical gastroenterology and hepatology : the official clinical practice journal of the American Gastroenterological Association. 2014 Dec;12(12):1964-72; quiz e119-20. doi: 10.1016/j.cgh.2013.09.055. Epub 2013 Oct 1.
  • Rana SV, Malik A. Hydrogen Breath Tests in Gastrointestinal Diseases. Indian journal of clinical biochemistry : IJCB. 2014 Oct; 29(4): 398–405. Published online 2014 Mar 21. doi: 10.1007/s12291-014-0426-4.
  • Ghoshal UC, Srivastava D, Ghoshal U, Misra A. Breath tests in the diagnosis of small intestinal bacterial overgrowth in patients with irritable bowel syndrome in comparison with quantitative upper gut aspirate culture. European journal of gastroenterology & hepatology. 2014 Jul;26(7):753-60. doi: 10.1097/MEG.0000000000000122.
  • Grace E, Shaw C, Whelan K, Andreyev HJ. Review article: small intestinal bacterial overgrowth--prevalence, clinical features, current and developing diagnostic tests, and treatment. Alimentary pharmacology & therapeutics. 2013 Oct;38(7):674-88. doi: 10.1111/apt.12456. Epub 2013 Aug 20.
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