14C-labelled glycocholate is administered orally. In the presence of bacterial overgrowth in the small bowel, extensive deconjugation of 14C-glycine occurs. The labelled glycine is rapidly absorbed and metabolised to 14C-carbon dioxide which is detected in the breath.
Deconjugation may also occur if the 14C-glycocholate reaches the colon. Bile salts are usually reabsorbed in the terminal ileum and such 'false' positive results may occur in patients with abnormal ileal function e.g. in Crohn's disease.