C - 14 BREATH TEST - XYLOSE (FOR INVESTIGATION OF ...



C - 14 BREATH TEST - XYLOSE (FOR INVESTIGATION OF BACTERIAL OVERGROWTH)

NOTE: WE ARE GENERALLY USING A NON RADIOACTIVE LACTULOSE HYDROGEN

BREATH TEST CURRENTLY.

[14C]-d-xylose breath test — Xylose is a pentose sugar that is catabolized by gram-negative aerobes, which are invariably part of the microflora implicated in bacterial overgrowth. Bacterial action on the sugar releases the radioactive isotope 14-CO2 which, after absorption, is detectable in breath samples. Only the one gram [14C]-d-xylose test is advocated for use in routine clinical practice by the Clinical Efficacy Committee of the American College of Physicians.

Compared to quantitative jejunal cultures, the sensitivity and specificity of the [14C]-d-xylose breath test approach 90 percent, values superior to other breath tests that have been used to diagnosis bacterial overgrowth [7]. However, lower values for sensitivity and specificity have been found in some studies [8]. Disorders associated with impaired gastric emptying may lead to false negative results, while rapid intestinal emptying may lead to false positive results due to early presentation of the test substrate in the colon. To optimize the diagnostic performance of the [14C]-d-xylose test, advocates recommend the following modifications:

  [pic] Patients with severe dysmotility syndromes have breath samples taken up to three hours after ingestion of the sugar.

  [pic] Patients undergo testing with the coadministration of intestinal transit markers to serve as a measure of intestinal transit time [9].

Although administration of 14-C is associated with trivial radiation exposure, it is not recommended for children or fertile women. A similar test based upon 13-C, which does not lead to radiation exposure, is under investigation [10]. The presence of lung disease may interfere with the interpretation of any breath test.

Breath hydrogen analysis — The principle of breath hydrogen testing is the administration of a test dose of carbohydrate (usually lactulose or glucose), which, in patients with bacterial overgrowth, is associated with a rise in breath hydrogen levels. The diagnostic accuracy of the glucose breath hydrogen test was recently compared to the d-xylose test and culture of the small bowel aspirate. There was found to be no statistically significant difference in accuracy between the studies [11]. Since the breath tests are simpler to perform they are a reasonable choice for screening and monitoring of therapy.

To improve accuracy of the test:

  [pic] Certain foods (bread, pasta, fiber) need to be avoided prior to testing because they cause prolonged hydrogen secretion.

  [pic] Cigarette smoking or physical exercise sufficient to produce hyperventilation needs to be avoided for two hours prior to testing.

  [pic] Oral bacteria may lead to an early hydrogen peak; thus, pretest mouth-washing with an antiseptic should be performed.

  [pic] Two consecutive hydrogen measurements should be obtained.

Breath hydrogen testing is safe, easy to perform, and can be used in women of child-bearing age and children. However, the usefulness of the test is limited by its lower sensitivity and specificity than the [14C]-d-xylose test because of the following circumstances:

  [pic] Lung disease may interfere with the interpretation of results.

  [pic] The hydrogen peak occurring from bacterial overgrowth in the distal small intestine may be difficult to discriminate from the normal peak seen when the test substrate reaches the colon.

  [pic] Rapid delivery of the test substrate to the colon in patients with short bowel syndrome may lead to false positive results [12].

  [pic] False negatives may occur in 30-40 percent of patients due to low anaerobic organism counts [13].

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