Increased accuracy of the carbon-14 D-xylose breath test in detecting small-intestinal bacterial overgrowth by correction with the gastric emptying rate

Diagnosis by Microbial Culture, Breath Tests and Urinary Excretion Tests, and Treatments of Small Intestinal Bacterial Overgrowth

Small intestinal bacterial overgrowth (SIBO) is characterized as the increase in the number and/or alteration in the type of bacteria in the upper gastrointestinal tract and accompanies various bowel symptoms such as abdominal pain, bloating, gases, diarrhea, and so on. Clinically, SIBO is diagnosed by microbial culture in duodenum/jejunum fluid aspirates and/or the breath tests (BT) of hydrogen/methane gases after ingestion of carbohydrates such as glucose. The cultural analysis of aspirates is regarded as the golden standard for the diagnosis of SIBO; however, this is invasive and is not without risk to the patients. BT is an inexpensive and safe diagnostic test but lacks diagnostic sensitivity and specificity depending on the disease states of patients. Additionally, the urinary excretion tests are used for the SIBO diagnosis using chemically synthesized bile acid conjugates such as cholic acid (CA) conjugated with para-aminobenzoic acid (PABA-CA), ursodeoxycholic acid (UDCA) conjugated with PABA (PABA-UDCA) or conjugated with 5-aminosalicylic acid (5-ASA-UDCA). These conjugates are split by bacterial bile acid (cholylglycine) hydrolase. In the tests, the time courses of the urinary excretion rates of PABA or 5-ASA, including their metabolites, are determined as the measure of hydrolytic activity of intestinal bacteria. Although the number of clinical trials with this urinary excretion tests is small, results demonstrated the usefulness of bile acid conjugates as SIBO diagnostic substrates. PABA-UDCA disulfate, a single-pass type unabsorbable compound without the hydrolysis of conjugates, was likely to offer a simple and rapid method for the evaluation of SIBO without the use of radioisotopes or expensive special apparatus. Treatments of SIBO with antibiotics, probiotics, therapeutic diets, herbal medicines, and/or fecal microbiota transplantation are also reviewed.

Reduced ¹³C-D-xylose absorption in alcoholics is more likely caused by alterations in small intestinal mucosa than delayed gastric emptying

OBJECTIVE

Alterations of the small intestinal absorptive surface are a probable cause of D-xylose malabsorption in chronic alcoholism. Delayed gastric emptying, however, may influence the (13)C-D-xylose breath test, which is used to study intestinal function in alcoholics. The aim of this study was to measure gastric emptying in alcoholics to elucidate whether retention of the test meal could explain the malabsorptive pattern of the (13)C-D-xylose breath test observed in alcoholics.

MATERIAL AND METHODS

Fifteen alcoholics performed the (13)C-octanoic acid and the (13)C-D-xylose breath tests on consecutive days in a random order. The (13)CO(2) expired was measured every 30 or 15 min for 4 h in the (13)C-D-xylose and the (13)C-octanoic acid breath tests, respectively, using a mass spectrometer equipped with a gas chromatograph. Test meals consisted of 100 mg of (13)C-D-xylose and 5 g of unmarked D-xylose dissolved in 250 ml water and 91 mg (13)C-octanoic acid embedded in a one-egg omelette served with white bread with margarine, respectively.

RESULTS

The alcoholic patients had a lower (13)C-D-xylose breath index compared with healthy controls (p < 0.0001). None of the (13)C-octanoic acid breath test variables, T(50%), T(max), T(lag), or GEC revealed any significant differences between the groups.

CONCLUSION

The pathological (13)C-D-xylose breath test in this group of alcoholics is unlikely to be caused by delayed gastric emptying. Malabsorption is the probable cause of the pathological (13)C-D-xylose breath test results in alcoholics.

Small intestinal bacterial overgrowth

Small intestinal bacterial overgrowth (SIBO) syndrome is characterized in its florid form by diarrhoea and weight loss. The most common underlying factors are dysmotility, small intestinal obstruction, blind or afferent loops. Small intestinal bacterial overgrowth can be diagnosed by: 1) culture of jejunum aspirate for bacterial counts, 2) 14C-D-xylose breath testing, 3) non-invasive hydrogen breath testing using glucose or lactulose or 4) 14C-glycocholic acid breath testing. The treatment usually consists of the eradication of bacterial overgrowth with repeated course of antimicrobials, correction of associated nutritional deficiencies and, when possible, correction of the underlying predisposing conditions.

A systematic review of diagnostic tests for small intestinal bacterial overgrowth

BACKGROUND

A growing number of studies seem to suggest that small intestinal bacterial overgrowth (SIBO) is a common clinical problem. Although various techniques are available to make this diagnosis, tradition has accepted small bowel aspirate (>10(5) cfu/ml) as a gold standard. In this systematic review, the validity of culture and other diagnostic testing for SIBO is evaluated.

METHODS

We performed a systematic review of the literature from 1966 to present using electronic databases (PubMed and OVID). Full paper review of those abstracts that fulfilled preset criteria was carried out to evaluate the validity of various tests in diagnosing SIBO. Finally, all papers were evaluated against published standards for studies on diagnostic testing.

RESULTS

Seventy-one papers met the criteria for detailed review. Studies were very heterogeneous with regards to patient populations, test definitions, sample size, and methods in general. Small bowel colony counts appeared elevated in most gastrointestinal diseases compared to controls. The traditional definition of >10(5) cfu/ml was usually indicative of stagnant loop conditions. Although, numerous diagnostic tests were studied, not even culture papers met the quality standards described by Reid et al. Breath testing and other diagnostic testing suffered therefore from the lack of a gold standard against which to validate in addition to the poor quality.

CONCLUSIONS

There is no validated diagnostic test or gold standard for SIBO. In this context, the most practical method to evaluate SIBO in studies at this time would be a test, treat, and outcome technique.

Evaluation of small bowel bacterial overgrowth

Small bowel bacterial overgrowth historically has been associated with malabsorption syndrome attributed to deconjugation of bile acids in the upper small intestine. Recent reports raise the possibility that bacterial overgrowth may be a cause of watery diarrhea or irritable bowel syndrome. Quantitative culture of jejunal contents has been the gold standard for diagnosis, but a variety of indirect tests have been developed (and mostly discarded) over the years in an attempt to facilitate the diagnosis of small bowel bacterial overgrowth. These include breath tests and biochemical tests based on bacterial metabolism of various substrates. Problems with these indirect tests include rapid transit, which may cause substrate to reach the luxuriant bacterial flora in the colon, producing false positives and vagaries of the tests themselves, which may produce falsely negative results. The perfect test for small bowel bacterial overgrowth is yet to be devised.

D-xylose testing

The literature on D-xylose testing has been reviewed, stressing advances in our understanding of absorption in general (including D-xylose absorption), the relationship of D-xylose testing to the development of excellent serologic tests for the diagnosis of celiac disease, the use of D-xylose testing in the evaluation of diarrhea in acquired immunodeficiency syndrome, new information on breath testing for the evaluation of malabsorption, and recent information on the understanding of D-xylose absorption compared with transcellular vs. paracellular transport. The authors suggest ways in which D-xylose testing might be employed in malabsorption or diarrhea evaluations, including some algorithms.