Crohn's disease and ulcerative colitis are the two main forms of inflammatory bowel disease, and both can cause troubling and persistent digestive symptoms. Several tests are used to build a picture of what is going on, though the final diagnosis always rests with a specialist. Understanding what each test looks for can make the process feel less daunting.
What inflammatory bowel disease is
Inflammatory bowel disease (IBD) describes long-term conditions in which the digestive tract becomes inflamed. Crohn's disease can affect any part of the gut from mouth to bottom and often involves patches of inflammation, while ulcerative colitis affects the large bowel and rectum in a more continuous pattern. Both tend to flare and settle over time.
Typical symptoms to be aware of include:
- Persistent or recurring diarrhoea
- Abdominal pain and cramping
- Blood or mucus in the stool
- Fatigue and feeling generally run down
- Unintended weight loss
The tests used to investigate
No single blood or stool test diagnoses IBD by itself, but together they raise or lower the level of suspicion and guide the next step. The commonly used tests include:
- Faecal calprotectin — a stool test that detects inflammation in the bowel wall and is often the lead investigation
- Full blood count — can reveal anaemia or a raised platelet count, both of which can accompany active inflammation
- CRP and ESR — general markers of inflammation in the body
- Ferritin — reflects iron stores, which can fall if there is ongoing blood loss from the gut
How IBD differs from IBS
It is easy to confuse IBD with irritable bowel syndrome (IBS) because they share symptoms such as changeable bowel habits and abdominal discomfort. The essential difference is inflammation: IBD involves genuine, measurable inflammation of the bowel, whereas IBS does not. This is why a marker like faecal calprotectin can be so helpful in pointing your doctor in the right direction.
Check for gut inflammation
A faecal calprotectin test flags bowel inflammation, the first step in investigating IBD.
Check for gut inflammationHow a diagnosis is confirmed
If the tests suggest inflammation, the next step is usually referral to a gastroenterologist. Diagnosis is confirmed with a colonoscopy, which allows the specialist to look directly at the bowel lining, and a biopsy, where small tissue samples are examined under a microscope. This combination confirms whether IBD is present and helps distinguish Crohn's disease from ulcerative colitis, which in turn shapes treatment.
Blood and stool tests are therefore best thought of as signposts. They help decide who needs specialist investigation and can be useful for monitoring, but they do not replace the definitive tests done by a specialist.
When to seek help
Please see a doctor promptly if you have diarrhoea lasting more than a couple of weeks, blood in your stool, unexplained weight loss, persistent abdominal pain, or symptoms that wake you at night. Seek urgent care if you feel severely unwell, are becoming dehydrated, or have severe pain. Testing supports your assessment, but worrying symptoms always need to be reviewed by a doctor.
Check for gut inflammation
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Specialist interest: Cardiovascular Medicine · OneMedicine, CQC-registered clinic