Faecal bile acids – is there an easier test to detect bile acid diarrhoea?
A common condition often misdiagnosed
One million people in the UK are affected by bile acid diarrhoea (BAD), but many sufferers are not aware of the term or understand what’s causing their symptoms. This common condition – also known as bile acid malabsorption – is a form of chronic diarrhoea, characterised by erratic and urgent loose bowel motions, with painful abdominal cramping. It’s often misdiagnosed as a symptom of irritable bowel syndrome, and is also frequently missed when present in the context of inflammatory bowel disease. If left untreated, BAD can cause weight loss, gallstones and kidney stones.
What causes bile acid diarrhoea?
After bile acids are made in the liver, they travel to the stomach and small intestine to help digestion, primarily to aid the absorption of fats. The majority of bile acids are then absorbed back into the bloodstream to be returned to the liver for reuse at the next mealtime. Failure by the body to recycle bile acids happens when either production exceeds absorption capacity, or when there has been damage to the small intestine due to disease, surgery or radiotherapy. When this process fails, excess bile acids enter the lower intestine, triggering fluid to be pumped into the colon, which leads to looser stools and urgency to pass motions.
Difficulties diagnosing bile acid diarrhoea
One of the possible reasons that BAD is often misdiagnosed or missed is that, until now, there has only been one diagnostic test available, which is only performed in a few centres across the UK. The ‘gold standard’ SeHCAT test (seleno-tauro-homocholic acid test) involves digestion of a capsule containing bile salts and a radioactive tracer; the patient undergoes two gamma scans, one week apart. Bile acids are then measured at the second scan, and the percentage of acids remaining in the stool indicates whether the patient has excreted an excessive amount during the week, and therefore has BAD.
SeHCAT testing is mostly carried out in larger, city hospitals with nuclear medicine departments. Travelling long distances, twice, to have a diagnosis confirmed can be time consuming and inconvenient for many patients. This often prompts doctors to simply prescribe the sequestrant medication used to treat BAD, foregoing the step of establishing a formal diagnosis.
The challenges of treating without confirmation of cause
Given this ‘blind’ approach to treatment, it is inevitable that a certain number of patients will end up taking medication that they don’t need – and won’t help their diarrhoea – with studies suggesting that this could account for up to a third of all sequestrant prescriptions. Patient compliance with treatment for BAD is also notoriously poor. Many people find the powdered medication unpalatable; it usually needs to be mixed in a drink and taken two or three times a day to be effective. One in four people prescribed the drug can’t tolerate the taste, or they find it worsens their symptoms, so they stop taking it.
The availability of a diagnostic test that is more locally available and easier for patients to access would likely increase the numbers referred for testing, helping to eliminate those patients who do not have BAD and cut out the practice of prescribing ineffective and unpleasant sequestrant treatments to individuals who don’t need it. Recognising the challenges associated with the current lack of diagnostic options, the National Institute for Health and Clinical Excellence (NICE) has highlighted the need for cheaper and safer tests to identify BAD.
A promising alternative
A novel faecal bile acid (FBA) test designed specifically to address this issue has recently been developed. This enzymatic assay analyses concentrations of serum 7α-hydroxy-4-cholesten-3-one (C4) in a single stool sample, with a raised level indicating that the patient is suffering from BAD. Although only recently launched, results so far show good correlation with findings from SeHCAT testing. Crucially, it does not involve exposing the patient to radiation. The patient doesn’t even need to leave their own home for testing, instead simply sending a sample to a local diagnostic lab for routine biochemistry testing. This allows results to be provided far more promptly, and testing to be repeated whenever clinically indicated. An FBA-positive result means that treatment for BAD can start without hospital testing or admission, reducing the need for costly and resource-heavy tests and appointments.
Larger scale studies into the diagnostic accuracy of this test are underway, but the FBA test already represents a useful tool to assist patient selection for referral to SeHCAT testing, or to indicate which patients may benefit from sequestrants. It can also be used for therapeutic monitoring – providing a baseline measure of faecal bile acids before starting treatment, and allowing the success of treatment to be measured a few months down the line.
Confirmation of the presence of excess bile acids before starting medication will allow doctors to give a more thorough explanation to patients about the cause of their diarrhoea. This helps lead the patient to a greater understanding of what the treatment is targeting, and should increase compliance with medication regimes, ultimately improving patient comfort and reducing healthcare costs.
For more information or to try the FBA test, go to www.biohithealthcare.co.uk/BAD