Comparison of the proportion of unconjugated to total serum cholic acid and the [¹⁴C]-xylose breath test in patients with suspected small intestinal bacterial overgrowth

Abstract

The proportion of unconjugated to total cholic acid in fasting serum and the 1-gram [¹⁴C]-xylose breath test were determined in 36 patients with suspected bacterial overgrowth of the small intestine. Twenty-two patients had an abnormal [¹⁴C]-xylose breath test, indicating bacterial overgrowth. The proportion of unconjugated to total cholic acid was significantly higher in the patients with an abnormal breath test compared with those displaying a normal breath test (47 ± 5% vs 16 ± 3%). A good correlation was obtained between the proportion of unconjugated to total cholic acid and the breath test (r = 0.63, n = 36). Provided the [¹⁴C]-xylose breath test is reliable as a test of bacterial overgrowth, determination of the proportion of unconjugated to total cholic acid in fasting serum had a sensitivity of 73% and a specificity of 94%. It is suggested that determination of the proportion of unconjugated to total cholic acid in peripheral venous blood may be useful as a simple screening test for detection of bacterial contamination of the upper small intestine provided the patients do not have bile acid malabsorption.

Key Words:

• bile acid
• bacterial overgrowth
• breath test
• chenodeoxycholic acid
• unconjugated bile acid:xylose