Clinical application of a selenium (75Se)-labelled bile acid for the investigation of terminal ileal function

With the introduction of a selenium bile acid SeHCAT (tauro-23-75Se-Selena-25 homocholic acid) a new and clinically valuable test for the functioning of the terminal ileum has been made available. Previous studies have shown that the test detects patients with bile acid malabsorption due to ileal disease. In this study SeHCAT retention was evaluated in nine patients with Crohn's disease and in seven healthy controls after intravenous administration of 0.15 MBq (4 muCi). A simple way of expressing the results is proposed. By using the calculated time required to eliminate 50% of the SeHCAT (WBR50), information is obtained as to the degree of terminal ileum malfunction regarding bile acid absorption. Accurate values seem to be achieved within 48 hours. As the SeHCAT is a gamma-ray emitter the dose retained could be measured by external counting. We suggest a practical design for the test using a simple scintillation spectro-photometer with a single detector in a low-background room. In patients and healthy controls the SeHCAT retention as calculated by WBR50 was 63 hrs (15-163) and 120 hrs (range 99-141), respectively. There was no overall relation between SeHCAT elimination and the intestinal transit time, although in the patient group a significant correlation was demonstrated, probably secondary to the impairment of the terminal ileum. A significant correlation was shown between the outcome of the test and the faecal excretion of total bile acids.