Persistent diarrhoea, urgency, abdominal pain, and bloating naturally point towards IBS with diarrhoea (IBS-D). In most cases, that’s the right diagnosis. However, those symptoms are not unique to IBS.

Bile acid diarrhoea (BAD) is an important alternative explanation. The condition occurs when too many bile acids enter your colon, drawing water into the bowel and causing diarrhoea. It’s estimated that around 25% to 33% of people investigated with apparent IBS-D have evidence of BAD.

If diarrhoea persists despite treatment, further IBS testing can help investigate whether IBS is really responsible or another digestive problem is causing similar symptoms.

What Is Bile Acid Diarrhoea?

Bile acids are normally produced by the liver, stored in the gallbladder, and then released into the small intestine to help digest fat.

Once their job is done, they’re mostly reabsorbed towards the end of the small bowel. However, that’s not always the case. If too much is excreted or not enough is absorbed, the excess can draw fluid into the large intestine, producing diarrhoea.

Known as bile acid diarrhoea, it’s a common alternative to IBS-D. The term bile acid malabsorption is sometimes used. Technically, that’s not accurate as true malabsorption is linked to ileal disease or resection.

Bile Acid Diarrhoea Symptoms vs IBS-D

Bile acid diarrhoea and IBS-D can look very similar. Both conditions can cause loose stools, urgency, bloating, and abdominal discomfort. However, there are some differences in the typical symptom pattern.

IBS-D commonly causes:

• abdominal pain or cramping linked to bowel movements

• frequent loose stools

• bloating and excess wind

• changes in how often you need to open your bowels

• periods where symptoms improve or worsen

Bile acid diarrhoea more commonly causes:

• very loose or watery diarrhoea

• sudden, pronounced urgency

• diarrhoea shortly after eating

• needing to open your bowels during the night

• occasional faecal incontinence

Bile acid diarrhoea can also be intermittent rather than occurring every day. These differences can raise suspicion of bile acid diarrhoea, but symptoms alone cannot reliably distinguish IBS-D from bile acid diarrhoea. Testing is usually needed to determine the underlying cause.

Why Is Bile Acid Diarrhoea Mistaken for IBS-D?

IBS is one of the most common intestinal conditions. It’s estimated that IBS affects 4–5% of UK adults. IBS-D accounts for roughly one-third to two-fifths of cases, which means IBS-D affects over 1% of the entire UK population.

It’s therefore not surprising that when a patient presents with diarrhoea, bloating, and stomach discomfort, most doctors think of IBS-D first.

BAD produces many of the symptoms, so someone with BAD can simply appear to have IBS-D. But it’s important to consider other conditions. BAD is more likely with:

• Crohn's disease affecting the terminal ileum

• surgery removing part of the ileum

• previous pelvic radiotherapy

• following gallbladder removal

What Is a SeHCAT Test?

The SeHCAT test is a diagnostic test for bile acid diarrhoea. A patient swallows a capsule containing a synthetic bile acid with a very small radioactive tracer. A scan measures how much is present initially, and then again seven days later.

If only a small proportion of the tracer remains after seven days, it suggests the bile acid has not been reabsorbed normally. The result thresholds are normally:

• 10–15% retention: mild bile acid loss

• 5–10%: moderate

• below 5%: severe

What Happens If You Have Bile Acid Diarrhoea?

Bile acid diarrhoea can often be treated directly. The main treatments are bile acid sequestrants that bind bile acids in the intestine so they cannot pull water into the colon. The most common bile acid sequestrants are cholestyramine and colesevelam.

Some patients may also be advised to make dietary changes. Because bile acid is released after eating fatty foods, reducing dietary fat may help.

This is why diagnosis is so important. All treatments for IBS are symptom specific. They will not solve the underlying problem if the condition is actually BAD.

When Should Persistent Diarrhoea Be Investigated?

Persistent diarrhoea shouldn’t automatically be assumed to be IBS. Given that BAD is found in a substantial proportion of people investigated for apparent IBS-D, it’s worth investigating for bile acid diarrhoea as well as other conditions.

Testing can include blood tests, stool tests, and specialist investigations designed to look for causes including inflammation, infection, coeliac disease, and bile acid diarrhoea.

If you've been diagnosed with IBS-D but treatment isn't controlling your symptoms, further investigation may help identify another cause. Book an appointment with The Functional Gut Clinic to explore specialist testing to help rule out some other possible causes for persistent diarrhoea.

Have a look at the upcoming article: IBS and Alcohol: Why Drinking Triggers Symptoms and How to Manage It