Aim To investigate whether patients follow advice regarding the duration of a fast, prior to blood tests which require an overnight fast for their correct interpretation.

Method Patients referred for a glucose-tolerance test gave informed consent. They were asked to complete a questionnaire regarding the duration of their fast, and an additional blood sample was collected for fasting total bile-acid measurement.

Results 184 patients were recruited. The median duration of fast self reported by patients was 14 h (range 12–26 h). Total bile-acid concentrations were within the fasting reference range except for six individuals. The median total bile-acid concentration found was 2.1 μmol/l (range 0.1–19.5 μmol/l).

Conclusion All patients who self-reported a duration of fast reported a fast recognised as being adequate for fasting blood tests. This was confirmed in almost all by low normal total bile-acid measurements, which were well within the fasting range.