Why is BAD underdiagnosed?

Graham Johnson, Managing Director at BIOHIT Ltd

Bile acid diarrhoea (BAD) is a condition that affects approximately one to two per cent of the UK population, and up to one third of patients with diarrhoea-predominant irritable bowel syndrome (D-IBS).¹ This makes it more prevalent than some better-known conditions of the gut – such as Crohn’s and ulcerative colitis – with a similar incidence to coeliac disease.¹ Despite being considered a common disorder in the world of gastroenterology, BAD diagnosis is often delayed or missed, leaving patients with debilitating symptoms that significantly impact their quality of life, including faecal incontinence, excessive flatulence, and frequent, urgent, watery diarrhoea. Here, we discuss the current challenges of diagnosing these patients, and a simple, cost-effective test that could be slotted into current care pathways to help shed some light on this underdiagnosed condition.

The uncelebrated gut condition

BAD is caused by an excess of bile acids in the small intestine – either due to malabsorption or excessive secretion – which results in diarrhoea when reaching the colon. Bouts of diarrhoea are often accompanied by pain and urgency, and symptoms sometimes spread beyond the gastrointestinal tract to more general feelings of tiredness, general malaise and anxiety. There is currently no known cure for BAD, but effective diet and pharmaceutical treatments to manage and control the symptoms are available.

BAD is typically diagnosed in secondary care by specialist gastroenterologists, however, it is somewhat of a problem child in primary care, and is often managed quite differently between physicians. When a patient presents to their GP with chronic idiopathic diarrhoea, they can expect to endure a long journey of investigations while multiple potential causes are excluded. Whilst there are limited tools available to positively identify BAD in primary care, it is seldom on the radar early in the investigational journey, due to a general lack of awareness amongst doctors and patients. GPs do have access to a battery of first-line tests to help rule out other, more well-known causes – such as coeliac disease, inflammatory bowel disease, malabsorption, immunodeficiency, infection and cancer – but often the diagnosis of BAD is made in secondary care, much further down the line after specialist referral.

When the patient is investigated in secondary care, the gastroenterologist will normally start by ruling out the obvious – or potentially more serious – conditions. This can mean repeat tests for the patient and re-treading old ground. When BAD is suspected, in the absence of an easily accessible diagnostic test, doctors will sometimes choose to treat empirically with bile acid sequestrants and/or a low-fat diet to see if they can resolve the symptoms. In some patients this works, however, pharmaceutical treatments for BAD are reported by many patients as unpleasant, unpalatable and difficult to tolerate, and so it’s vital to have a firm diagnosis, which gives patients the impetus to adhere to their medication, as there is more chance that it is correctly prescribed and will improve their condition.

Limitations of the current care pathway

The traditional care pathway for adult patients presenting with chronic diarrhoea without red flag symptoms is long and arbitrary. It usually involves a physical examination and a combination of diet, lifestyle and family history assessments, as well as routine blood tests, coeliac serology and faecal tests for calprotectin and infections, all of which are often negative in a BAD patient. Physicians may also rule out the possibility of exocrine pancreatic insufficiency, or only query the possibility of BAD in cases where there is raised suspicion, such as patients who have undergone radiation therapy or previous surgery – for example, terminal ileum resection or cholecystectomy – or have Crohn’s disease. After this long clinical work-up with no positive indications of the cause of the symptoms, the BAD patient is generally referred for a colonoscopy, which is again likely to be negative unless associated with the predisposing conditions mentioned above.

Diagnosis of BAD, therefore, is often missed or severely delayed, or sometimes misdiagnosed as IBS, as there is no obvious cause or access to convenient diagnostic tests. In fact, research has shown that up to 44 per cent of patients whose BAD is misdiagnosed as IBS may suffer with symptoms for five years.² This significantly increases the cost of care per case and prolongs the morbidity associated with the disorder.

One test currently available for the diagnosis of BAD is the ⁷⁵Selenium taurocholic acid (SeHCAT) scan. SeHCAT is a radiopharmaceutical that incorporates a ⁷⁵Se gamma-emitter and a taurine-conjugated bile acid analogue. Following ingestion, a patient’s retention of the SeHCAT molecule is measured using a gamma camera, which helps to investigate enterohepatic circulation of bile acids. Although currently considered the gold standard method for diagnosis of BAD, it is not widely accessible, and is only available in nuclear medicine departments – which are sparsely located –requiring two visits over seven days to complete. Furthermore, it is not approved in some countries, including the US, where the alternative route of testing for faecal bile acids is routinely used to help diagnose BAD. This protracted pathway can be upsetting for the patient who, during this time, is still suffering from the same incapacitating symptoms, and the situation is made worse by bottlenecks that are common to both gastroenterology and nuclear medicine services, resulting in long waiting lists and slow access.

Reconstructing the pathway

The latest guidelines advocate a formal testing strategy for the investigation of chronic diarrhoea,³ and to avoid empirical treatments. This is an encouraging step towards the wider recognition of BAD, and shines the light on newer diagnostic tests that could help to improve the time to diagnosis. By the time the patient is referred for further, specialist investigation, they have often already had one or two faecal tests – e.g. calprotectin and pancreatic elastase – and we believe the answer could lie in the same stool sample.

The IDK^® Faecal Bile Acids test is a photometric assay used to quantify faecal bile acids for the diagnosis of BAD in patients with D-IBS, or to support differential diagnosis. This test is designed to reinforce and streamline the current care pathway for the benefit of both the patient and the healthcare system. It can be incorporated with early investigations where, if the faecal calprotectin test is negative, the same stool sample can be used to test for faecal bile acids as a ‘reflex’ test. No one likes producing or handling a stool sample, but this one-step approach allows physicians to gain more information from a single sample without additional consultation, potentially preventing further unnecessary and intrusive procedures – such as the SeHCAT scan and colonoscopy – or directing the patient to alternative treatments or investigations.

The availability of the IDK Bile Acids test in primary care offers a rapid option to help eliminate BAD as the possible cause of symptoms. A delayed diagnosis doesn’t just significantly impact a patient’s life, but it is also costly to the healthcare system. In fact, BAD is misdiagnosed in up to 30 per cent of patients with D-IBS, and delays are thought to double the overall cost of diagnosis.⁴ At around £15 per test – compared to nearly £400 for a SeHCAT scan, and more than £500 for a colonoscopy – examining faecal bile acids early in the care pathway offers a cost-effective solution to help signpost patients for further investigation and get diagnosed sooner.

Turning the BAD into… better

Although not life threatening, BAD is a lifelong and extremely upsetting condition, where patients often end up housebound in fear of faecal incontinence or not finding a toilet when they need one. Treatments are effective, however, patients often go through a long rigmarole to find what’s causing their diarrhoea. Shortening the pathway is therefore crucial to improve patient outcomes at an earlier stage, and this can now more easily begin at the very first consultation in primary care.

To find out more about BIOHIT IDK Bile Acids test, visit:

www.biohithealthcare.co.uk/biohit-product/faecal-bile-acids-assay-idk/

References

1. Walters JR, Pattni SS. Managing bile acid diarrhoea. Therap Adv Gastroenterol. 2010;3(6):349-357. doi:10.1177/1756283X10377126
2. Fernandes DCR, Poon D, White LL, et al. What is the cost of delayed diagnosis of bile acid malabsorption and bile acid diarrhoea?. Frontline Gastroenterol. 2019;10(1):72-76. doi:10.1136/flgastro-2018-101011
3. Arasaradnam RP, Brown S, Forbes A, et al. Guidelines for the investigation of chronic diarrhoea in adults: British Society of Gastroenterology, 3rd edition. Gut. 2018;67(8):1380-1399. doi:10.1136/gutjnl-2017-315909
4. Farrugia A, Arasaradnam R. Bile acid diarrhoea: pathophysiology, diagnosis and management. Frontline Gastroenterol. 2021;12:500-507. doi:10.1136/flgastro-2020-101436