SIBO: Small Intestinal Bacterial Overgrowth

What is SIBO and could it be causing my IBS?

SIBO is defined as the presence of excessive gut microbes in the small intestine that originate from the large intestine. Thought to be responsible for Irritable Bowel Syndrome (IBS) in many individuals, there is much symptom overlap - eg bloating, flatulence, diarrhoea, constipation, abdominal pain, nausea and even fibromyalgia - with other gastrointestinal disorders such as coeliac disease, lactose intolerance, Crohn’s disease and other inflammatory bowel disease (IBD). Identifying causes of gastrointestinal disorders can prove challenging.


SIBO Breath Test and SIBO Blood Test


Breath Testing for SIBO ~ Aerodiagnostics Laboratory

A SIBO Breath test measures hydrogen and methane gases produced by microbes in the small intestine that have diffused into the blood, then the lungs, for expiration.  These gases are produced by bacteria, yeast or archaea, not by humans, and are tracked on a graph over the small intestine transit time of 2-3 hours.  A SIBO-experienced clinician can then interpret the data to help determine type and duration of therapy required.

A sugar solution of glucose or lactulose is taken after a 1 or 2 day preparatory diet (see below). This diet removes much of the food that would feed the bacteria, allowing for a clear reaction to the sugar drink.  There are two types of breath test: lactulose and glucose.  Please ensure you choose the correct challenge agent (lactulose or glucose) when ordering. Further details below, but first consider the alternative SIBO testing method – using blood.


Blood Testing for SIBO

Recent advances in SIBO Testing include the Cyrex Array 22: Irritable Bowel / SIBO Screen™, which uses blood samples to consistently identify the presence of SIBO. It is well recognised that the breath tests, lactulose/glucose, are not completely reliable; they render many false positives and many false negatives. Furthermore, breath tests, whilst providing much helpful information, can be problematic to carry out successfully. Consequently Cyrex Array 22 has been developed as a blood test for assisting in the determination of IBS-SIBO. Whilst blood testing for SIBO does not distinguish between the microbial gases, this test may be more accurate in many cases in identifying SIBO presence.

It is extremely useful to run this test on any individual who wishes to identify/confirm the presence of SIBO-IBS, either as a standalone test and/or to confirm results of the breath test. It is also arguably the only way that SIBO can be identified/confirmed in children, for whom the breath test is not recommended. An added advantage of the Cyrex blood test for SIBO is that there is no requirement for a preparatory diet.  Note that this blood test does not distinguish between methane-producing and hydrogen-producing microbes.


Glucose Breath Test
Humans and bacteria all absorb dietary glucose, and ingested glucose should be absorbed within the first three feet of the small intestine (SI). Therefore if the bacterial gases hydrogen and/or methane are produced during the glucose breath test, it reflects an overgrowth in the proximal/upper end of the SI (within the first two feet).  This test successfully assesses proximal SI overgrowth, but cannot assess distal overgrowth which is thought to be more common. If this test comes back negative, then it would be worth running the lactulose breath test to assess the lower portion of the SI.


Lactulose Breath Test
Lactulose is a non-digestible sugar to humans:  Only bacteria can metabolise it, and they then produce gas.  If there is an overgrowth, this will be reflected in the levels of hydrogen or methane gases.   Lactulose takes longer to metabolise than glucose and can therefore help assess the entire length of the small intestine including the distal end which is not included by the glucose challenge.


Which Test to Choose

Breath testing is less expensive than blood testing, but can result in false negatives. Furthermore, it can be difficult for children to produce satisfactory breath samples. The blood test is preferable for collecting samples from children, and many adults prefer it because it does not require a preparation diet.

In summary of the two breath tests, the glucose test is thought to be more sensitive in measuring SIBO as compared to the lactulose test, but only if SIBO has infected the first 2-3 feet of the small intestine. The lactulose test is more likely to identify SIBO infection in the lower SI, but it is less accurate overall. If you're considering running SIBO breath tests, it is often worth doing both lactulose and glucose, and if there is still some doubt, confirming with Cyrex blood test for SIBO-IBS.


How to do SIBO Breath Tests

The breath tests are performed at home. There should be a 24-48 hour preparation period prior to starting the test, which should be started with a 12 hour preparation diet followed by a 12 hour overnight fast. The breath-collection process will take 3 hours; the samples need to be collected according to the specified timed intervals. 


Preparation Diet for SIBO Breath Test


The following guidelines serve as indications as to what is required in terms of advance preparations for SIBO Breath Tests, but please refer to your kit's specific instructions at least 48hrs prior to collecting breath samples


Before you start the breath test, a 24-48 hour preparation is required consisting of a minimum 12 hour restricted diet and a 12 hour fasting period (overnight). Breath samples are then collected every 20 minutes for 3 hours total (1 baseline/control sample & 9 breath samples after ingesting either a Glucose or a Lactulose solution, depending on which test you are running).


Things to know before you start:

  • Do not conduct this test if you have an acute infectious illness or atypical diarrhoea.
  • Wait at least 1 month after if you have had a colonoscopy, Barium study or enemas before conducting the test.
  • Wait at least 2 weeks from your last dose of antibiotics,  antifungals or probiotics (including yoghurts) before starting the test.
  • One week prior to testing please avoid proton pump inhibitors (PPI) for reflux (eg: omeprazole etc), laxatives, stool softeners and/or stool bulking agents, as well as the use of antacids and any other over the counter medication or supplements / herbs that contain fibre or promote bowel movements.
  • Continue to take all other medication prescribed by your doctor, for example blood pressure drugs, cholesterol lowering drugs, thyroid drugs, etc.
  • One day prior to testing, please stop vitamins, minerals and supplements including digestive aids such as enzymes or hydrochloric acid.
  • Do not smoke (including second-hand smoke), for at least 1 hour before or at any time during the breath test.
  • No sleeping or vigorous exercise for at least 1 hour before or at any time during the breath test.


Important information:

This test uses glucose or lactulose as its testing agent, and is not recommend for individuals who have had allergic reactions to lactulose, or for diabetics with a fasting urine glucose concentration >105mg/dl, or who are on a galactose/lactose-restricted diet.


Why is the preparation diet so important?

The SIBO breath test is a measure of gases produced by bacteria in the small intestine, having consumed a sugar-laden drink. Plant-based foods and lactose-containing foods will also feed these bacteria and they will produce these gases. By adhering to the diet, you will get a clear reaction to the sugary drink and ensure the accuracy and reliability of your results.


How long should the preparation diet be adhered to?

The preparation diet should be adhered to for a minimum of 24 hours prior to starting the test. Your practitioner may request you to follow this diet for 48 hours prior to starting the test if you are very constipated. Please check with your practitioner: it is their decision.


What to Eat: 1-2 days before your test

The ONLY acceptable foods for the preparatory diet are listed below – DO NOT EAT ANY FOOD THAT IS NOT ON THIS LIST. If you have allergy or intolerance to any of these foods, you SHOULD NOT eat them.

  • Baked or grilled chicken, fish or turkey (seasoned with salt and pepper only)
  • White bread (only white) – but do not eat it if you are gluten/wheat intolerant.
  • Plain steamed white basmati or jasmine rice (if you are on a grain free diet, please do not consume rice).
  • Eggs (cooked any way you prefer)
  • Clear chicken or beef broth with (no vegetables pieces, no bouillon, no bone broth or vegetable broth).
  • Olive oil / coconut oil for cooking (1 tbsp only)
  • Salt & pepper
  • You may drink plain still water, weak black coffee or weak black tea – WITHOUT adding sugar or artificial sweeteners or milk/cream.
  • NO green or herbal teas

If you are uncertain if something will affect the test, avoid the product or consult your practitioner prior to starting the test.


12 hours before starting your test

Begin fasting: DO NOT eat or drink anything, except water.


Example Timetable:

You can establish your own time-frames but as an example:


From 8am – 8pm of the day before the test:

Breakfast: scrambled eggs (made without dairy)

Mid morning snack: chicken broth

Lunch: chicken with white rice seasoned with salt and pepper

Mid afternoon snack: chicken broth

Dinner: fish and white rice seasoned with salt and pepper

Drinks: water

From 8pm – 8am: FASTING – you can drink water during this time.


The Day of the Test

  • Wake up at least 1 hour prior to beginning the sample collection. You may brush your teeth as normal, but do not have breakfast. No smoking or vigorous exercise for at least one hour prior to or during sample collection. You may drink water throughout the breath test in moderation.
  • Follow the instructions within the test kit for preparing the test solution
  • Ensure that you adhere strictly to the collection times specified in the guidelines


Once collected: Keep collected specimens at room temperature until you are ready to dispatch them.



Test Details:


Test name(s):

  • SIBO with Lactulose Breath Test: Small Intestinal Bacterial Overgrowth – Lactulose
  • SIBO with Glucose Breath Test: Small Intestinal Bacterial Overgrowth – Glucose


  • Aerodiagnostics Laboratory via Nordic VMX


Specimen Requirements:

  • Breath samples according to patient guidelines within test kits


Costs - Accurate at July 2021

  • Lab Analysis Fees:
    • SIBO Lactulose Test: £179
    • SIBO GlucoseTest: £179
  • Test Kit Return Shipping Fees:
    • £16 (Up to 1 kg in weight) UK Mainland
    •  Other countries – please enquire below.


More info on SIBO blood testing by following this link:


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