Unconjugated serum bile acids as a marker of small intestinal bacterial overgrowth

Abstract

Non-invasive methods to detect small intestinal bacterial overgrowth often lack specificity in patients who have undergone an ileal resection or have an accelerated intestinal transit. Since elevated serum unconjugated bile acid levels have been found in patients with clinical signs of bacterial overgrowth, we studied the clinical value of unconjugated serum bile acids as a marker of small intestinal bacterial overgrowth. Patients with culture-proven bacterial overgrowth had significantly elevated fasting unconjugated serum bile acid levels (median and range: 4.5; 1.4-21.5 mumol l-1) as compared to healthy subjects (0.9; 0.3-1.7 mumol l-1, P less than 0.005), to persons with an accelerated intestinal transit (1.0; 0.3-1.9 mumol l-1, P less than 0.005) and to persons who have undergone an ileal resection (2.1; 0.7-3.6 mumol l-1, P less than 0.005). The same was true 30 and 60 min after ingestion of a Lundh meal. Serum unconjugated bile acid levels above 4 mumol l-1 were found in eight of 10 patients with culture-proven small intestinal bacterial overgrowth whereas serum levels above 4 mumol l-1 were found in none of the patients from the three control groups. These results suggest that determination of unconjugated serum bile acids is of clinical value in the evaluation of patients suspected of small intestine bacterial overgrowth.

Serum Unconjugated Bile Acids and Small Bowel Bacterial Overgrowth in Pediatric Intestinal Failure: A Pilot Study

“…When we compare our results to these previously determined thresholds, we see that the proportion of SUBA in our controls (22%) does approximate the expected value of 18% in healthy children, whereas children with history of IF and suspected SBBO had a much higher of fraction of SUBA at 87%. Absolute concentration of SUBA was higher as well in IF subjects compared with controls but only 5 of 14 IF subjects exceeded the proposed cutoff of 4 μM/L for SBBO described in adults by Masclee et al (1 of 11 controls did surpass 4 μM/L). Among these 5 IF subjects, however, 4 did have positive aspirates for SBBO.…”

“…Elevated SUBA has been previously reported in adults with SBBO and is attributed to increased intestinal bacterial deconjugation of intraluminal bile acids in the presence of SBBO. Bolt 15 The majority (8 of 10) had SUBA concentrations >4 μM/L. In contrast, none of the controls without SBBO had SUBA concentrations above this value.…”

“…Bolt et al found elevated postprandial SUBA concentrations in adults with SBBO diagnosed by [ 14 C] glycocholate breath test . Additionally, Masclee et al found SUBA to be elevated in adults with SBBO diagnosed by jejunal fluid aspirate . The majority (8 of 10) had SUBA concentrations >4 μM/L.…”

Comparison of Direct and Indirect Tests for Small Intestinal Bacterial Overgrowth and Antibiotic-Responsive Diarrhea in Dogs

“…Previous studies in humans have documented unconjugated bile acids in intestinal fluid and serum, and increased concentrations are thought to be an indirect indicator of SIBO. [13][14][15][16][17][18][19] To date, only 1 study has measured serum total unconjugated bile acid (TUBA) concentrations in dogs. 20 That study suggested that such measurements could prove to be a more sensitive and specific test for SIBO than measurement of serum folate and cobalamin.…”

Evaluation of small bowel bacterial overgrowth

“…Although unconjugated bile acid is cleared efficiently by the liver, levels tend to be higher than normal in patients with small bowel bacterial overgrowth [16]. This approach has not been accepted widely due to technical difficulty in measuring bile acid concentrations in blood [17] and due to potential confounding effects of liver disease and ileal bile acid malabsorption, which may lead to exposure of colonic bacteria to increased amounts of bile acid.…”