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    2 The diagnostic tests

    Clinical need and practice

    2.1 In bile acid diarrhoea, a form of chronic diarrhoea, the body does not recycle bile acids properly. It is most commonly caused when bile acids are overproduced in people who have no damage to the bile acid recycling system. Bile acid diarrhoea can also be a secondary condition, if the small bowel or another part of the bile acid recycling system is damaged, for example by disease or surgery.

    2.2 Symptoms of bile acid diarrhoea are usually managed with bile acid sequestrant medication. Three products are available: colestyramine, colestipol and colesevelam.

    The intervention


    2.3 SeHCAT (tauroselcholic [75 selenium] acid) is a diagnostic radiopharmaceutical capsule used to measure how well the body absorbs bile acids. It contains 75 selenium (a gamma emitter) and a synthetic bile acid (tauroselcholic acid). When swallowed, the body absorbs SeHCAT like a natural bile acid. It can be detected in the body by a scan using a gamma camera.

    2.4 A SeHCAT test involves 2 outpatient appointments in a hospital's nuclear medicine department. At the first appointment (day 1), the person swallows a SeHCAT capsule, waits for up to 3 hours and has a baseline scan. At the second appointment (day 7), they have a follow-up scan. People may need to stop anti-diarrhoeal medication for the duration of the test because it may affect the result.

    2.5 The test result shows how much SeHCAT remains in the body. To calculate this, the amount of radioactivity detected in the follow-up scan is divided by the amount of radioactivity detected in the baseline scan. Bile acid diarrhoea is usually diagnosed when around 15% or less SeHCAT remains in the body.

    The comparators

    2.6 The comparators are:

    • no SeHCAT testing and no bile acid sequestrants

    • no SeHCAT testing and a trial of bile acid sequestrants.