Irritable bowel syndrome is real, common and miserable — and it is also, by definition, a diagnosis made only after more serious conditions have been reasonably excluded. The patients who concern me most in clinic are not those with dramatic symptoms; they are those who self-diagnosed IBS years ago, or were given the label after a brief consultation, and have been managing a changing symptom picture under an old diagnosis ever since. Bowel cancer, inflammatory bowel disease, coeliac disease and microscopic colitis are all routinely discovered in patients who arrived saying "it's just my IBS".
What IBS legitimately looks like
Recurrent abdominal pain linked to opening the bowels, associated with a change in stool frequency or form, often with bloating that builds through the day, fluctuating over months to years, frequently tracking stress and specific foods — beginning, typically, in the teens to thirties. Symptoms that fit this picture, in the absence of any feature below, very rarely represent anything sinister.
The red flags — any one of these takes you out of the IBS box
- Blood in or on the stool, or black tarry stools — never IBS, always explained
- Unintentional weight loss
- Symptoms that wake you from sleep — nocturnal pain or diarrhoea is not an IBS feature
- Unexplained anaemia or iron deficiency on blood tests
- A new, persistent change in bowel habit over the age of about 45–50 — IBS rarely makes its debut in later life; something that looks like new IBS at 55 is investigated as something else until proven otherwise
- Fever, or a family history of bowel cancer or inflammatory bowel disease
- A positive FIT test (the stool blood test used in screening and GP assessment)
- Progressive, steadily worsening symptoms — IBS fluctuates; it does not march in one direction
What investigation actually involves
Far less than most patients fear. The first line is non-invasive: blood tests (blood count, inflammation markers, coeliac screen), a stool inflammation test (faecal calprotectin — excellent at separating IBS from inflammatory bowel disease) and a FIT test for hidden blood. Many patients are confidently reassured on these alone. Where red flags or abnormal results point onward, colonoscopy is the definitive examination — direct inspection of the entire large bowel, with removal of any polyps in the same sitting. I am JAG dual-accredited in colonoscopy and gastroscopy and perform these weekly at Nuffield Health Warwickshire; the procedure takes about thirty minutes under sedation, and patients consistently report it was far easier than the anticipation. A normal colonoscopy, incidentally, is not a wasted test: a secure IBS diagnosis transforms how confidently it can be managed.
Two modern complications of the picture
Weight-loss injections: millions now take GLP-1 medicines whose side effects mimic IBS closely — and which can mask or mimic other conditions too. That tangle is unpicked in is it the injection or is it IBS? Age drift: patients correctly diagnosed with IBS at 25 sometimes coast on that label at 55, when the same symptoms would trigger investigation in a new patient. An old IBS diagnosis does not cover new or changed symptoms — the red flags apply at every age, every time the picture shifts.
The rule worth remembering
IBS is common, benign and manageable. The red flags above are uncommon, important and short enough to memorise. Symptoms that fit IBS with none of them: manage with confidence. Any single one of them: investigate first, label afterwards. The cost of checking is a clinic visit and perhaps a half-day procedure; the cost of a wrong label can be measured in stages of disease.
Frequently asked questions
How do I know if it's IBS or something serious?
IBS causes fluctuating pain linked to bowel habit, with bloating, typically from a young age. Red flags pointing beyond IBS include bleeding, weight loss, nocturnal symptoms, anaemia, fever, a family history of bowel disease, or new persistent symptoms after about 45 — any one warrants investigation.
Can IBS start after 50?
Genuinely new IBS rarely makes its first appearance in later life. A new, persistent change in bowel habit over 45–50 is investigated — usually with FIT testing, blood tests and often colonoscopy — before an IBS label is applied.
Does IBS cause blood in the stool?
No. Visible blood, or black tarry stools, is never explained by IBS and always requires assessment. Causes range from haemorrhoids to inflammation to cancer — most are benign, but the distinction must be made, not assumed.
What is the faecal calprotectin test?
A simple stool test measuring bowel inflammation. Normal results make inflammatory bowel disease very unlikely and support an IBS diagnosis; raised results direct onward investigation, usually colonoscopy. It is a cornerstone of modern non-invasive bowel assessment.
Do I need a colonoscopy to diagnose IBS?
Not always — typical symptoms in a younger patient with normal blood, stool and FIT tests can be confidently diagnosed without one. Red flags, abnormal tests or onset over 45 are the usual triggers for colonoscopy.