What’s the Most Accurate SIBO Breath Test for Diagnosis?

Glucose Breath Test vs. Lactulose Breath Test for SIBO

Key Takeaways

  • Glucose breath tests are more accurate than lactulose breath tests for the diagnosis of small intestinal bacterial overgrowth (SIBO).
  • Elevations of methane or hydrogen after 90-100 minutes usually show bacteria in the large intestine, which is normal. Misreading this can lead to false positives.

There are two types of SIBO breath tests: lactulose breath tests and glucose breath tests. The lactulose test is generally more popular, but the data indicate it’s not the as accurate.

What is the best test for small intestinal bacterial overgrowth (SIBO)? Let’s discuss.

SIBO breath test: lady holding a fruit on each hand

What Is SIBO?

Small intestinal bacterial overgrowth (SIBO) is exactly what the name implies: an excess of normal gut bacteria in the small intestine. Symptoms of SIBO include:

  • Gas or flatulence
  • Bloating
  • Abdominal pain
  • Altered bowel function, including diarrhea, constipation, or other alterations in transit time
  • Weight loss or nutritional deficiencies from malabsorption
  • Food intolerances, such as lactose intolerance or fructose malabsorption
SIBO breath test: What is SIBO?

New evidence suggests there may also be a correlation with symptoms like heartburn [1]. 

SIBO has also been correlated with irritable bowel syndrome (IBS ) [2 Trusted SourcePubMedGo to source, 3 Trusted SourcePubMedGo to source], fibromyalgia [4], rheumatoid arthritis [5 Trusted SourcePubMedGo to source], non-responsive celiac disease [6 Trusted SourcePubMedGo to source], inflammatory bowel diseases (IBD), including Crohn’s disease [7 Trusted SourcePubMedGo to source], rosacea [8 Trusted SourcePubMedGo to source], and metabolic health issues like being overweight, high blood sugar, and high cholesterol [9 Trusted SourcePubMedGo to source, 10 Trusted SourcePubMedGo to source, 11]. And, surprisingly, one study showed that being hypothyroid was a risk factor for SIBO as well [12].

Abdominal adhesions from injury or surgery [13 Trusted SourcePubMedGo to source], chronic constipation [14 Trusted SourcePubMedGo to source] [15 Trusted SourcePubMedGo to source], use of proton pump inhibitors (PPIs) [16 Trusted SourcePubMedGo to source], and small intestinal diseases [17 Trusted SourcePubMedGo to source, 18 Trusted SourcePubMedGo to source] are recognized as common causes of SIBO. So, it’s not a surprising contention that imbalances in the digestive system — in this case, SIBO — may correlate with many symptoms and conditions. This is why it can be very helpful to have a diagnostic test to tell you whether you have small intestinal bacterial overgrowth.

SIBO Breath Testing

The most practical and clinically available tests for diagnosing SIBO are two types of breath tests: glucose breath tests and lactulose breath tests.

To prepare for a methane or hydrogen breath test for SIBO, the patient either drinks a glucose solution or a lactulose solution and then collects breath samples with an at-home breath test kit. The lab measures the levels of hydrogen and methane gas in the samples, which was produced in the small intestine.

Best SIBO Breath Test? A Meta-Analysis Review

If you’re planning to run a SIBO breath test, you’ll want to use the highest quality test. Thankfully, a meta-analysis — a summary of all available high-quality data on a subject — has been published to give a definitive answer about which breath test is best for the diagnosis of SIBO. The paper is titled “Breath Test for Non-Invasive Small Intestinal Bacterial Overgrowth Diagnosis: A Systematic Review with Meta-Analysis” [19 Trusted SourcePubMedGo to source].

Glucose Breath Test vs. Lactulose SIBO Breath Testing

The authors of the meta-analysis concluded, “Overall, our results clearly showed that glucose breath tests had higher sensitivity and specificity than lactulose breath tests” [20 Trusted SourcePubMedGo to source]. 

  • Sensitivity tells you if you were correctly diagnosed with the condition.
  • Specificity tells you if you were correctly found not to have that condition.
Comparison of two types of SIBO breath tests according to sensitivity and specificity

In the study, glucose breath tests showed a sensitivity of 58% and a specificity of 83%, compared to 42% sensitivity and specificity at 70% for lactulose breath tests [21 Trusted SourcePubMedGo to source].

The lower these numbers, the higher the likelihood of false negatives or false positives.

The meta-analysis data clearly show the glucose breath test has better scores for sensitivity and specificity, meaning it correctly diagnoses those who have the condition, and it correctly identifies who does not have the condition more often.

This is very relevant because patients are frequently incorrectly diagnosed with SIBO and are then subjected to unnecessary fear, dietary restrictions, and treatments.

This is likely because the lactulose breath test — while helpful in the hands of an astute clinician who uses it correctly — actually suffers from a higher number of false positives. This is the most commonly used SIBO breath test.

In this context, the glucose breath test has better sensitivity and specificity than the lactulose breath test and, therefore, should be preferred in clinical practice.

Lactulose Breath Test and False Positives

One of the challenges with the lactulose breath test is in the time interpretation of the test. This is a common error that leads to incorrect SIBO diagnosis.

Here is what a typical SIBO breath test result looks like: 

SIBO breath test: Positive Lactulose Breath Test

Test samples are collected at either 15- or 20-minute intervals. When looking at the lactulose breath test, it’s important to identify at what point you no longer see readings from the small intestine.

Research indicates the preferred window is 80-90 minutes [22 Trusted SourcePubMedGo to source], but you could go up to 100 minutes. The 80- or 90-minute mark generally shows the transition to the large intestine. This matters because rising gas levels in the large intestine are normal.

Unfortunately, SIBO lab analyzers haven’t really caught up with this interpretation. So, it’s important that clinicians understand the correct time interpretation.

People who have a gas elevation at 100 or 120 minutes, and sometimes even at 140 minutes, may be falsely told they have SIBO. They may then be prescribed  SIBO treatment with antibiotics like Rifaximin when they really need nothing of the sort.

Clinicians need to be stringent with the time interpretation of the lactulose breath test in order to mitigate this false positive rate.

If you’re using a lactulose breath test, it’s important to not be overly liberal in diagnosing SIBO, especially if the only elevation of gases is seen towards the end of the test.

Glucose Breath Test Advantages

The glucose breath test seems to protect against that false positive. 

I feel this is very important for patients to understand because this update hasn’t yet permeated the SIBO community. While most providers have the best intentions when diagnosing, it seems some patients are told they have SIBO when they don’t. This is a problem because it subjects people to unnecessary fear, worry, and take on potentially dietary restrictions and treatments.

image of a stethoscope

How Useful Are SIBO Breath Tests?

The overall utility of SIBObreath testing is moderate. It can help to steer decisions, but it’s not the end-all-be-all.

The meta-analysis authors concluded though breath tests don’t perform as well as the gold-standard testing, they are useful because they are less expensive and invasive [23 Trusted SourcePubMedGo to source].

So essentially, though SIBO breath testing is imperfect, it’s probably the most justifiable test compared with sampling jejunal secretions by endoscopy.

We can only test for some of the imbalances we know exist in the small intestine, which means it’s not in the best interest of patients or providers to overly focus on testing.

We can use testing as part of the process to determine what may be going on, but we can also use many therapies for treating SIBO without lab results. 

Probiotics are one example. They can be effective and helpful for small intestine bacterial overgrowth and other microbiome imbalances [24 Trusted SourcePubMedGo to source]. One meta-analysis and several clinical trials show probiotics can be an effective treatment for SIBO [25 Trusted SourcePubMedGo to source, 26 Trusted SourcePubMedGo to source, 27 Trusted SourcePubMedGo to source]. You don’t need a SIBO breath test to use a probiotic for IBS or SIBO symptoms.

The same likely applies for Small Intestinal Fungal Overgrowth (SIFO), since probiotics also have antifungal effects.

SIBO Breath Testing: Bottom Line

SIBO breath testing can be helpful, but it has limitations. Of the SIBO breath tests, the glucose breath test is best. However, a well-trained clinician can responsibly use a lactulose test.

➕ References
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