Serum unconjugated bile acids in patients with small bowel bacterial overgrowth

Concentrations of total and unconjugated bile acids in serum were measured fasting and 2 h postprandially in 9 patients with a positive [14C]glycocholate breath test consistent with small bowel bacterial overgrowth and in 13 controls. Gas-liquid chromatography-mass spectrometry (GLC-MS) and enzymatic-fluorometric assays were both used. In contrast to previous work, total serum bile acids were only occasionally elevated in patients with bacterial overgrowth. Total 2 h postprandial unconjugated bile acids, however, were elevated in 7/9 patients when measured by GLC-MS and in 6/9 when measured by the enzymatic-fluorometric method. The best separation between patients and controls was achieved by GLC-MS determinations of 2 h postprandial unconjugated cholic acid or primary bile acids, which were abnormal in 8/9 patients. This study indicates that measurement of serum bile acids may be a useful approach to the diagnosis of bacterial overgrowth, but would require accessible methods for separating and measuring cholic acid or unconjugated primary bile acids in post-prandial sera.