SIBO Test
The SIBO test detects bacterial overgrowth in the small intestine through analysis of exhaled breath after ingesting a sugar-rich substrate.
General Description
The SIBO test (Small Intestine Bacterial Overgrowth) is a procedure used to determine whether there is bacterial overgrowth in the small intestine, typically due to bacteria from the large intestine migrating upstream. This bacterial excess can lead to reduced gastric acid levels, anatomical alterations, or changes in gastrointestinal motility.
This procedure is also commonly known as the breath test, as it measures hydrogen (H2) and methane (CH4) in exhaled air. In healthy individuals, sugar fermentation in the large intestine produces hydrogen and methane, which partially enter the bloodstream and are mostly exhaled through the breath. However, in patients with SIBO, a rapid increase in methane or hydrogen can be detected in exhaled air at specific times, for example, after ingesting lactulose or fructose. This phenomenon is utilized to diagnose the condition, making the SIBO test essentially a hydrogen and methane breath test, colloquially known as the breath test.
The hydrogen and methane breath test not only diagnoses bacterial overgrowth but also provides information on other conditions, such as malabsorption or sugar intolerance.
When is it indicated?
The SIBO test is indicated when there is no clear explanation for the following symptoms:
- Bloating
- Abdominal distension
- Excess gas
- Abdominal pain
- Fatigue
- Diarrhea
- In some cases, constipation
- Unexplained weight loss or gain
- Vitamin deficiencies
Certain conditions, such as diabetes, hypothyroidism, scleroderma, Crohn's disease, or amyloidosis, increase the risk of developing SIBO. In these cases, performing a hydrogen and methane breath test is particularly relevant for diagnosis.
How is it performed?
The SIBO test consists of two distinct but similar phases. A baseline sample is first collected to determine the patient’s normal breath gas levels while fasting, which serves as a reference for subsequent measurements after ingesting a sugar substrate.
The procedure is as follows:
- After resting for a few minutes while seated in the waiting area, the patient exhales into a tube connected to a collection bag.
- The patient then ingests a sugar solution (usually lactulose or glucose dissolved in water) and exhales into a separate tube. It is important not to wait more than ten minutes between ingesting the substrate and collecting the second sample.
- The patient returns to the waiting area and remains as calm as possible.
- Eight additional breath samples are collected at intervals of 20–30 minutes.
Once the samples reach the laboratory with proper identification, they are analyzed using a gas chromatograph, which measures hydrogen and methane concentrations in each bag. The results are displayed in a graph, allowing the specialist to compare baseline levels with subsequent readings. When sugar ferments in the large intestine, H2 and CH4 are produced; therefore, early detection of these gases indicates fermentation in the small intestine. Generally, an increase in hydrogen and methane within the first 120 minutes suggests bacterial overgrowth.
Risks
The SIBO test is considered safe and does not pose health risks.
What to expect from the SIBO test
The SIBO test is neither painful nor uncomfortable, although adherence to preparation instructions is crucial to avoid altering results.
On the day of the appointment, patience and a distraction are recommended during waiting periods, as excessive movement, eating, or smoking is not allowed. The total test duration is approximately 3 hours.
Results usually take 5–10 days, depending on the laboratory and test type. If positive, the specialist will explain the findings and propose a treatment plan or additional tests if necessary.
Specialties in which the SIBO test is required
The SIBO test is performed in the laboratory by specialists in clinical analysis and clinical biochemistry. It is commonly requested Family and community medicine, Gastroenterology, or Endocrinology and Nutrition.
How to prepare
Strict preparation is essential, as deviations may alter test results. The specialist will provide detailed instructions in the days leading up to the test:
- One month prior: avoid antibiotics.
- Five days prior: avoid enemas.
- 48 hours prior: avoid:
- Laxatives
- Antidiarrheal medications
- Probiotics
- Prokinetic agents
- 24 hours prior: avoid:
- Cereals, bread, cookies, toast, rusks, and pancakes
- Pastries, sweets, jams, and bakery products
- Legumes, vegetables, and potatoes
- Fruits, juices, and nuts
- Cold cuts and processed meats
- Soft drinks
- Alcoholic beverages
Allowed: - Eggs
- White rice (without garlic, onion, or tomato sauce)
- Unprocessed cold cuts (e.g., serrano or Iberian ham)
- Meat
- White or oily fish
- Water, coffee, tea, or unsweetened infusions
- Dairy products
- Day of the test:
- Fast for 12 hours (water allowed)
- Do not smoke within 12 hours
- Do not brush teeth; antiseptic mouth rinse is allowed the night before and the morning of the test
