Dietary interference with the use of Bilitec to assess bile reflux.

The Bilitec probe, which uses bilirubin as a marker for the detection of duodeno-oesophageal reflux, is subject to interference from strongly coloured foods, which can cause erroneously high bilirubin absorbance readings. To overcome this problem it is necessary to ingest a diet that is free from such substances. We tested the bilirubin absorbance of 32 different food substances in an in vitro environment, including many of the foods that are currently recommended for consumption during Bilitec studies. 'Dry' foods were blended with water, 'non-dry' solid foods were blended undiluted, and breakfast cereals were blended with milk. Blended mixtures were then tested for bilirubin absorption either undiluted or after mixing with hydrochloric acid. The 'absorbance' of weakly coloured foods was usually less than the commonly accepted threshold of 0.14, and the 'absorbance' of strongly coloured foods was usually above this. The 'absorbance' of three substances was higher in an acid environment. Three of the currently recommended foods had a sufficiently high 'absorbance' to interfere with readings in the clinical situation. Of the 32 substances tested, only 13 are suitable when the 'absorbance' threshold is set at 0.14. This number can be increased to 19 if the threshold is increased to 0.20. From the foods evaluated, enough are suitable at the 0.14 threshold to enable a suitable diet to be constructed for most patients. Furthermore, many potentially acceptable foods remain untested. Clarification of appropriate food substances will help patients to be aware which foods are safe to eat, so that food interference can be prevented during Bilitec studies.