Irritable bowel syndrome is one of the most common gut conditions, affecting a large slice of the population at some point. It brings a mixture of tummy pain, bloating and changeable bowel habits — sometimes diarrhoea, sometimes constipation, often both at different times. IBS is real and can be genuinely disruptive, but it is what doctors call a diagnosis of exclusion: it is reached once other conditions with similar symptoms have been ruled out.
Why "ruling out" comes first
Several conditions can mimic IBS, and some need specific treatment. Blood tests do not diagnose IBS itself — there is no positive IBS blood marker — but they help confirm that nothing else is being missed. Reassuringly normal results support an IBS diagnosis and allow you to focus on managing symptoms with confidence.
The bloods commonly used
When investigating suspected IBS, a doctor will often consider:
- Coeliac antibody screen — coeliac disease can look very like IBS, so it is important to exclude (and you must be eating gluten for the test to be accurate).
- Full blood count — to check for anaemia, which can suggest bleeding or malabsorption.
- Inflammation markers (CRP and ESR) — raised levels can hint at inflammatory bowel disease rather than IBS.
- Thyroid function — an overactive or underactive thyroid can disturb bowel habit.
A stool test for calprotectin is also often used to help distinguish IBS from inflammatory bowel disease, as it reflects inflammation in the gut wall.
The gluten point for coeliac testing
Because coeliac disease overlaps so closely with IBS, testing for it is a key step. The catch is that the coeliac blood test only works if you are eating gluten at the time. If you have already gone gluten-free hoping to ease your symptoms, the test can be falsely negative. Keep eating a normal, gluten-containing diet until testing is done, and discuss any dietary changes with a clinician first.
Rule out other causes
A coeliac antibody screen helps exclude one of the most common IBS mimics before an IBS diagnosis is made — remember to keep eating gluten beforehand.
Book a coeliac screenRed flags that need prompt attention
Certain symptoms are not typical of IBS and should prompt you to see a doctor without delay. These include unexplained weight loss, rectal bleeding or blood in the stool, a persistent change in bowel habit especially after the age of 50, difficulty swallowing, a tummy or back-passage lump, symptoms that wake you at night, or a family history of bowel or ovarian cancer. Anaemia found on a blood test is another reason for further assessment. These features warrant proper investigation rather than being assumed to be IBS.
Managing IBS once confirmed
Once other conditions are excluded, IBS is usually managed with dietary adjustments (a structured low-FODMAP approach with a dietitian can help), regular routines, stress management and, where needed, medication for specific symptoms. Knowing that the serious causes have been ruled out is often a relief in itself and makes these strategies easier to commit to.
Rule out other causes
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Specialist interest: Cardiovascular Medicine · OneMedicine, CQC-registered clinic