A survey of the clinical use of SeHCAT in the UK

SeHCAT (tauroselcholic [75selenium] acid) for the investigation of bile acid diarrhoea in adults: a systematic review and cost-effectiveness analysis

Background

Tauroselcholic [75selenium] acid (SeHCAT™) (GE Healthcare, Chicago, IL, USA) is a radiopharmaceutical that may be useful in diagnosing bile acid diarrhoea.

Objectives

To assess the clinical effectiveness and cost-effectiveness of SeHCAT for the investigation of adults with chronic unexplained diarrhoea, diarrhoea-predominant irritable bowel syndrome or functional diarrhoea (suspected primary bile acid diarrhoea), and adults with chronic diarrhoea and Crohn’s disease who have not undergone ileal resection (suspected secondary bile acid diarrhoea).

Methods

Sixteen databases were searched to November 2020. The review process included measures to minimise error and bias. Results were summarised by primary or secondary bile acid diarrhoea and study quality was considered. The cost-effectiveness analysis combined a short-term (6-month) decision-analytic model (diagnosis and initial treatment response) and a lifetime Markov model comprising three health states (diarrhoea, no diarrhoea and death), with transitions determined by probabilities of response to treatment. Analyses were conducted from an NHS and Personal Social Services perspective.

Results

Twenty-four studies were included in this review. Of these, 21 were observational studies, reporting some outcome data for patients treated with bile acid sequestrants, and in which only patients with a positive SeHCAT test were offered bile acid sequestrants. The median rate of response to bile acid sequestrants, among patients with a 7-day SeHCAT retention value of ≤ 15%, was 68% (range 38–86%) (eight studies). The estimated sensitivity of SeHCAT (≤ 15% threshold) to predict positive response to colestyramine was 100% (95% confidence interval 54.1% to 100%) and the specificity estimate was 91.2% (95% confidence interval 76.3% to 98.1%) (one study). The median proportion of treated patients who were intolerant/discontinued bile acid sequestrants was 15% (range 4–27%) (eight studies). There was insufficient information to determine whether or not intolerance varied between colestyramine, colestipol and colesevelam. For both populations, the SeHCAT 15% (i.e. a SeHCAT retention value of ≤ 15%) strategy dominated other strategies or resulted in incremental cost-effectiveness ratios of < £20,000–30,000 per quality-adjusted life-year gained. For the suspected primary bile acid diarrhoea population, SeHCAT 15% was the strategy most likely to be cost-effective: 67% and 73% probability at threshold incremental cost-effectiveness ratios of £20,000 and £30,000 per quality-adjusted life-year gained, respectively. For the Crohn’s disease population, these probabilities were 89% and 92% at £20,000 and £30,000 per quality-adjusted life-year gained, respectively. Cost-effectiveness was mostly led by treatment response. SeHCAT 15% was the strategy with the highest response rate in the majority of scenarios explored.

Limitations and conclusions

There is a lack of evidence linking the use of SeHCAT testing to patient-relevant outcomes. The optimal SeHCAT threshold, to define bile acid diarrhoea and select patients for treatment with bile acid sequestrants, is uncertain. It is unclear whether or not patients with ‘borderline’ or ‘equivocal’ 7-day SeHCAT retention values (e.g. between 10% and 15%) and patients with values of > 15% could benefit from treatment with bile acid sequestrants. Although the results of the economic evaluation conducted for both populations indicated that the SeHCAT 15% strategy dominated the other two strategies or resulted in incremental cost-effectiveness ratios that were lower than the common thresholds of £20,000 or £30,000 per quality-adjusted life-year gained, the paucity and poor quality of evidence mean that uncertainty is high.

Future work

The optimum study design would be a multiarm randomised controlled trial, in which participants meeting the inclusion criteria are randomised to receive colestyramine, colestipol, colesevelam or placebo, and all participants receive SeHCAT testing.

Study registration

This study is registered as PROSPERO CRD42020223877.

Funding

This project was funded by the National Institute for Health and Care Research (IHR) Evidence Synthesis programme and will be published in full in Health Technology Assessment; Vol. 26, No. 45. See the NIHR Journals Library website for further project information.

Error analysis of collimated and uncollimated SeHCAT retention measurement using a gamma camera

AIM

There is increasing interest in using collimated gamma cameras for [75Se]tauroselcholic acid (SeHCAT) studies to image the distribution and to make use of the collimator pressure sensitive devices (PSD) for patient safety. However, the use of a collimator will substantially decrease the sensitivity of the gamma camera. The aim of this article is to enable departments to calculate the uncertainty of SeHCAT retention measurements so that the acquisition time can be optimised to perform a reliable SeHCAT study.

METHOD

We derive a mathematical equation from the first principles that can be used to calculate the uncertainty in SeHCAT retention measurements on the basis of Poisson counting statistics. The equation takes account of background subtraction, use of the geometric mean for anterior/posterior attenuation compensation and the day 7 to day 0 quotient calculation.

RESULTS

Uncertainties in SeHCAT retention measurement using an intrinsic (uncollimated) gamma camera counting for 100 s are very low, typically of the order 15 ± 0.1%. Uncertainties from collimated gamma camera counting significantly increase for the same 100 s counting duration: 15 ± 0.8% for slim patients and 15 ± 4% for obese patients.

CONCLUSION

The acquisition time must be increased for collimated gamma camera SeHCAT counting to achieve acceptable counting statistics for an acceptable total uncertainty in the SeHCAT retention measurement. For slim patients, a minimum counting time of 2 min is required. For larger patients, the acquisition time needs to be increased to 30 min and further increased to 50 min for obese patients.

Bile acid diarrhoea: pathophysiology, diagnosis and management

The actual incidence of bile acid diarrhoea (BAD) is unknown, however, there is increasing evidence that it is misdiagnosed in up to 30% with diarrhoea-predominant patients with irritable bowel syndrome. Besides this, it may also occur following cholecystectomy, infectious diarrhoea and pelvic chemoradiotherapy. BAD may result from either hepatic overproduction of bile acids or their malabsorption in the terminal ileum. It can result in symptoms such as bowel frequency, urgency, nocturnal defecation, excessive flatulence, abdominal pain and incontinence of stool. Bile acid synthesis is regulated by negative feedback loops related to the enterohepatic circulation, which are dependent on the farnesoid X receptor and fibroblast growth factor 19. Interruption of these feedback loops is thought to cause bile acid overproduction leading to BAD. This process may occur idiopathically or following a specific trigger such as cholecystectomy. There may also be an interplay with the gut microbiota, which has been reported to be significantly different in patients with severe BAD. Patients with suspected BAD are investigated in various ways including radionucleotide imaging such as SeHCAT scans (though this is not available worldwide) and blood tests. However, other methods such as bile acid measurement in stool (either spot test or 48 hours samples) and urine tests have been explored. Importantly, delay in diagnosis and treatment of BAD greatly affects patient's quality of life and may double the overall cost of diagnosis.

Prevalence of, and predictors of, bile acid diarrhea in outpatients with chronic diarrhea: A follow-up study

BACKGROUND

23-seleno-25-homo-tauro-cholic acid (SeHCAT) scanning to rule out bile acid diarrhea (BAD) in patients with chronic diarrhea has a high yield. Our previous study showed that patients with terminal ileal (TI) Crohn's disease, TI resection, or cholecystectomy were highly likely to have an abnormal scan. As a result, we encouraged clinicians to use a therapeutic trial of a bile acid sequestrant in these patients, instead of scanning. This may have reduced diagnostic yield of the test, so we examined this issue, as well as factors predicting an abnormal scan, in a large cohort of patients referred subsequently.

METHODS

We retrospectively identified 1,071 consecutive patients with chronic diarrhea undergoing SeHCAT scanning at Leeds Teaching Hospitals Trust from 2012 to 2016. We reviewed electronic patient records to obtain information on presenting gastrointestinal symptoms and any proposed risk factors for BAD. BAD was categorized according to subtype and severity.

KEY RESULTS

As expected, indications for scanning changed between 2012 and 2016, with a significant reduction in referrals with TI Crohn's disease or resection year-on-year (P < 0.001). Despite this, 457 (42.7%) patients had BAD and there was no downward trend in yield of SeHCAT during the 5 year period (P = 0.39). Overall, 51.6% had type II BAD, 36.1% type III, and 12.3% type I. BAD was mild in 31.7%, moderate in 34.4%, and severe in 33.9%. In total, 653 (61.0%) patients had no known risk factors, other than chronic diarrhea, but 233 (35.7%) of these individuals had BAD, and in 143 (61.4%), this was moderate or severe.

CONCLUSIONS AND INFERENCES

Despite reduced referrals for SeHCAT scanning in those with clear risk factors for BAD, the yield remained > 40%. One-third of those without known risk factors had BAD.

Long-term effect of medical treatment of diarrhoea in 377 patients with SeHCAT scan diagnosed bile acid malabsorption from 2003 to 2016; a retrospective study

BACKGROUND

Excessive amounts of bile acids entering the colon due to bile acid malabsorption cause chronic bile acid diarrhoea. Diagnosis is possible by measuring the retention fraction of orally ingested ⁷⁵ Selenium homotaurocholic acid (SeHCAT). The knowledge of long-term effects of medical treatment is sparse.

AIM

To describe diarrhoea, adherence to treatment, treatment effects and quality of life in a large, well-defined cohort of patients with bile acid diarrhoea.

METHODS

A retrospective survey was performed among 594 patients with bile acid malabsorption verified by SeHCAT scans at our unit between 2003 and 2016. Questionnaires about medical history, diarrhoea, use of medication, and quality of life scores were mailed to all patients.

RESULTS

Among 594 patients 377 (69%) responded. Among respondents, 121 (32%) had bile acid diarrhoea due to ileal disease or resection (type 1), 198 (52%) idiopathic bile acid diarrhoea (type 2) and 58 (16%) bile acid diarrhoea due to other non-ileal disease, mainly cholecystectomy (type 3). At follow-up, half of the patients, 184 (50%), reported improvement of diarrhoea. However, 273 patients (74%) still reported diarrhoea and 234 (62%) regularly used anti-diarrhoeal medication. In spite of treatment, 235 (64%) considered reduced quality of life by diarrhoea and 184 (50%) reported that diarrhoea was unaltered or worse than before established diagnosis.

CONCLUSION

Many patients with bile acid diarrhoea continue to have bothersome diarrhoea in spite of correct diagnosis and treatment.

Challenging current views on bile acid diarrhoea and malabsorption

BACKGROUND

In 2012, the National Institute for Health and Care Excellence (NICE) assessed guidance (DG7) on the use of tauroselcholic (⁷⁵selenium) acid (also known as SeHCAT) for the investigation of diarrhoea due to bile acid malabsorption (BAM) in patients with IBS-D and in patients with Crohn's disease who have not had an ileal resection. NICE concluded that tauroselcholic (⁷⁵selenium) acid was recommended for use in research only. NICE will be reviewing the decision to update the guidance for tauroselcholic (⁷⁵selenium) acid, for these populations, in March 2017.

AIM

Our aim is to summarise advances in BAM, also known as bile acid diarrhoea (BAD), and encourage clinicians to re-evaluate their understanding of this disorder.

APPROACH

We review the prevalence, diagnosis and treatment of BAD/BAM. We describe the new evidence available since the original NICE review in 2012, and discuss the economic issues associated with failure to diagnose or to treat BAD/BAM accurately.

EVIDENCE UPDATE

There is new and compelling evidence available since DG7, which shows that tauroselcholic (⁷⁵selenium) acid scanning is a powerful tool in the diagnosis of BAD/BAM. We summarise published prevalence data (approximately 1% prevalence in the UK, as suggested by clinical practice diagnosis rates), and highlight that the true prevalence of BAD/BAM could be far greater than this.

CONCLUSION

We present evidence that challenges current opinion about this disorder, and we commend both clinicians and health technology assessment (HTA) agencies for being open to arguments and new evidence in any future HTAs.

Incidence and predictive factors for positive 75SeHCAT test: improving the diagnosis of bile acid diarrhoea

AIMS

To determine the value of ⁷⁵SeHCAT retention in determining bile acid diarrhoea (BAD), treatment response and predictors of a positive result.

METHODS

Retrospective casenote review of consecutive patients undergoing ⁷⁵SeHCAT from 2008 to 2014, including gender, age, history, clinical, and laboratory parameters. This included diseases associated with Type 1 BAD (ileal resection, Crohn's disease) and Type 3 BAD. Chi-squared test and logistic regression determined factors predictive of BAD. Subjective response to treatment with bile acid sequestrants (BAS) was analysed with respect to the ⁷⁵SeHCAT result.

RESULTS

Of 387 patients, 154 (39.7%) were male and average age was 50 years. Ninety-five patients (24.5%) were investigated for Type 1 BAD, 86 (22.2%) for Type 3, and 206 patients (53.2%) for Type 2 or idiopathic BAD. There was a large increase in the number performed with time but no difference in percentage positive tests. One hundred and seventy-nine patients (46.2%) had BAD. Positive result was commonest in possible Type 1 and they had most severe BAD. Ninety-nine patients had severe BAD (<5% ⁷⁵SeHCAT retention), 47 moderate BAD (5% to <10% retention), and 33 mild BAD (10% to <15% retention). Predictors of a positive ⁷⁵SeHCAT were right hemicolectomy (OR 4.88), cholecystectomy (OR 2.44), and Crohn's (OR 1.86). A positive ⁷⁵SeHCAT predicted a good or partial response to BAS of 66.7% (mild), 78.6% (moderate), or 75.9% (severe BAD).

CONCLUSION

⁷⁵SeHCAT test use increased in 2008-2014, with high positive results throughout. Ileal resection, Crohn's, and cholecystectomy independently predict BAD. ⁷⁵SeHCAT predicted response to BAS.

Multicentre prospective survey of SeHCAT provision and practice in the UK

Objective

A clinical diagnosis of bile acid malabsorption (BAM) can be confirmed using SeHCAT (tauroselcholic (⁷⁵selenium) acid), a radiolabelled synthetic bile acid. However, while BAM can be the cause of chronic diarrhoea, it is often overlooked as a potential diagnosis. Therefore, we investigated the use of SeHCAT for diagnosis of BAM in UK hospitals.

Design

A multicentre survey was conducted capturing centre and patient-level information detailing patient care-pathways, clinical history, SeHCAT results, treatment with bile acid sequestrants (BAS), and follow-up in clinics. Eligible data from 38 centres and 1036 patients were entered into a validated management system.

Results

SeHCAT protocol varied between centres, with no standardised patient positioning, and differing referral systems. Surveyed patients had a mean age of 50 years and predominantly women (65%). The mean SeHCAT retention score for all patients was 19% (95% CI 17.8% to 20.3%). However, this differed with suspected BAM type: type 1: 9% (95% CI 6.3% to 11.4%), type 2: 21% (95% CI 19.2% to 23.0%) and type 3: 22% (95% CI 19.6% to 24.2%). Centre-defined ‘abnormal’ and ‘borderline’ results represented over 50% of the survey population. BAS treatment was prescribed to only 73% of patients with abnormal results.

Conclusions

The study identified a lack of consistent cut-off/threshold values, with differing centre criteria for defining an ‘abnormal’ SeHCAT result. BAS prescription was not related in a simple way to the SeHCAT result, nor to the centre-defined result, highlighting a lack of clear patient care-pathways. There is a clear need for a future diagnostic accuracy study and a better understanding of optimal management pathways.

Review article: bile acid diarrhoea - pathogenesis, diagnosis and management

BACKGROUND

Bile acid diarrhoea results from imbalances in the homoeostasis of bile acids in the enterohepatic circulation. It can be a consequence of ileal disease/dysfunction, associated with other GI pathology or can be idiopathic.

AIMS

To summarise the different types of bile acid diarrhoea and discuss the currently available diagnostic methods and treatments.

RESULTS

Bile acid diarrhoea is found in up to 40% of patients diagnosed as having functional diarrhoea/IBS-D, and in up to 80% of patients who have undergone ileal resection. It is likely under-diagnosed and under-treated. In idiopathic disease, errors in regulation feedback of fibroblast growth factor 19 contribute to the development of the condition. Clinical therapeutic trials for bile acid diarrhoea have been used to diagnose it, but the ⁷⁵ SeHCAT test is the primary current method. It is sensitive, specific and widely available, though not in the USA. Other diagnostic methods (such as serum measurement of the bile acid intermediate 7α-hydroxy-4-cholesten-3-one, or C4) have less widespread availability and documentation, and some (such as faecal measurement of bile acids) are significantly more complex and costly. First-line treatment of bile acid diarrhoea is with the bile acid sequestrant cholestyramine, which can be difficult to administer and dose due to gastrointestinal side effects. These side effects are less prominent in newer agents such as colesevelam, which may provide higher efficacy, tolerability and compliance.

CONCLUSION

Bile acid diarrhoea is common, and likely under-diagnosed. Bile acid diarrhoea should be considered relatively early in the differential diagnosis of chronic diarrhoea.

A Multicenter Prospective Study to Investigate the Diagnostic Accuracy of the SeHCAT Test in Measuring Bile Acid Malabsorption: Research Protocol

Background

Bile acid malabsorption (BAM) is one possible explanation for chronic diarrhea. BAM may be idiopathic, or result from ileal resection or inflammation including Crohn’s disease, or may be secondary to other conditions, including cholecystectomy, peptic ulcer surgery, and chronic pancreatitis. No “gold standard” exists for clinical diagnosis of BAM, but response to treatment with a bile acid sequestrant (BAS) is often accepted as confirmation. The SeHCAT (tauroselcholic [selenium-75] acid) test uses a radiolabeled synthetic bile acid and provides a diagnostic test for BAM, but its performance against “trial of treatment” is unknown. Fibroblast growth factor 19 (FGF-19) and 7-alpha-hydroxy-4-cholesten-3-one (C4) also offer potential new biomarkers of BAM.

Objective

This protocol describes a multicenter prospective study to evaluate the diagnostic accuracy of SeHCAT and 2 biomarkers in predicting BAM as assessed by trial of treatment.

Methods

Participating gastroenterology centers should have a minimum workload of 30 SeHCAT patients per annum. Patients should not be pregnant, on medication that could confound follow-up, or have any severe comorbidity. All eligible patients attending a gastrointestinal appointment will be invited to participate. On attending the SeHCAT test, blood and fecal samples will be collected for analysis of FGF-19 by enzyme-linked immunosorbent assay and for C4 and fractionated bile acids by liquid chromatography–mass spectrometry. A capsule containing radiolabeled SeHCAT will be administered orally and a scan performed to measure SeHCAT activity. Patients will return on day 7 to undergo a second scan to measure percentage SeHCAT retention. The test result will be concealed from clinicians and patients. BAS will be dispensed to all patients, with a follow-up gastroenterologist appointment at 2 weeks for clinical assessment of treatment response and adherence. Patients responding positively will continue treatment for a further 2 weeks and all patients will have a final follow-up at 8 weeks. The diagnostic accuracy of the SeHCAT test and biomarkers will be analyzed at different thresholds using sensitivity, specificity, positive and negative predictive value, likelihood ratios, and area under the curve in a sample of 600 patients. Multivariable logistic regression models will be used to assess the association between presence of BAM and continuous SeHCAT retention levels after adjustment for confounders.

Results

Funding is being sought to conduct this research.

Conclusions

The SeHCAT test for diagnosis of BAM has been in common use in the United Kingdom for more than 30 years and an evidence-based assessment of its accuracy is overdue. The proposed study has some challenges. Some forms of BAS treatment are unpleasant due to the texture and taste of the resin powder, which may negatively affect recruitment and treatment adherence. Trial of treatment is not as “golden” a standard as would be ideal, and itself warrants further study.

Bile acid diarrhoea and FGF19: new views on diagnosis, pathogenesis and therapy

Chronic diarrhoea induced by bile acids is common and the underlying mechanisms are linked to homeostatic regulation of hepatic bile acid synthesis by fibroblast growth factor 19 (FGF19). Increasing evidence, including that from several large case series using SeHCAT (selenium homocholic acid taurine) tests for diagnosis, indicates that bile acid diarrhoea (BAD) accounts for a sizeable proportion of patients who would otherwise be diagnosed with IBS. Studies of other approaches for diagnosis of BAD have shown increased bile acid synthesis, increased faecal levels of primary bile acids, dysbiosis and different urinary volatile organic compounds when compared with healthy controls or with other diseases. The role of the ileal hormone FGF19 in BAD has been strengthened: a prospective clinical study has confirmed low FGF19 levels in BAD, and so a test to measure these levels could be developed for diagnosis. In animal models, FGF19 depletion by antibodies produces severe diarrhoea. Bile acids affect colonic function through farnesoid X receptor (FXR) and TGR5 receptors. As well as these effects in the colon, FXR-dependent stimulation of ileal FGF19 production could be a logical mechanism to provide therapeutic benefit in BAD. Further studies of FGF19 in humans hold promise in providing novel treatments for this cause of chronic diarrhoea.

Recycling rate of bile acids in the enterohepatic recirculation as a major determinant of whole body 75SeHCAT retention

Measurement of the whole body retention of orally administered (75)SeHCAT is used to investigate patients with unexplained diarrhoea. Retention values of <15 % at 7 days post-administration are taken to indicate bile acid malabsorption (BAM). Whilst idiopathic BAM is frequently diagnosed with (75)SeHCAT, functional and morphological studies of the terminal ileum rarely show any abnormality, so the disorder may be more appropriately termed bile acid diarrhoea (BAD). In addition to malabsorption, excess bile acid may reach the colon, where the events leading to diarrhoea take place, as a result firstly of increased bile acid synthesis and secondly of an increased recycling rate of bile acids. Increased recycling has been largely ignored as a cause of BAD, but, as shown in this study, can readily result in excess bile acids reaching the colon even when ileal absorption efficiency is normal (i.e. 95-97 %). There needs to be a re-evaluation of the causes of BAD in patients without a history of previous intestinal resection or evidence of ileal pathology, such as Crohn's disease.