Get urgent medical help for heavy bleeding from the bottom, or, if you have Crohn's disease or ulcerative colitis, for many bloody bowel movements a day with fever, a racing heart or severe abdominal pain. These can signal a severe attack or complications that need hospital treatment.
Key points
- Irritable bowel syndrome (IBS) causes recurring abdominal pain with changes in bowel habit, but no visible damage to the gut. Inflammatory bowel disease (IBD), mainly Crohn's disease and ulcerative colitis, is immune-driven inflammation that can damage the bowel.
- Rectal bleeding, unintended weight loss, anaemia and a family history of bowel cancer or IBD point away from IBS and need investigation.
- Simple blood tests and a coeliac antibody test help confirm IBS. A stool test called faecal calprotectin can help separate IBS from IBD when cancer is not suspected.
- IBS is managed with diet, activity, symptom-targeted medicines and, if needed, psychological therapies. IBD needs specialist care, with steroids for flares and longer-term medicines, including biologics, to keep it in remission.
- NICE notes that IBS rarely starts for the first time at age 50 or older. New symptoms at that age deserve a closer look.
What they are
Irritable bowel syndrome
IBS is a disorder of gut-brain interaction. The US National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) explains that the gut becomes more sensitive and the bowel muscles contract differently, causing pain, bloating, diarrhoea, constipation or both. It is described by the main stool pattern: IBS with constipation (IBS-C), IBS with diarrhoea (IBS-D) or mixed (IBS-M). Some medicines help one type and worsen another. NIDDK reports that women are up to twice as likely as men to have IBS, and it is more common before age 50.
Crohn's disease
Crohn's disease can affect any part of the gut from mouth to anus, most often the end of the small intestine and the start of the large intestine. Common symptoms are diarrhoea, cramping abdominal pain and weight loss, with tiredness, fever, anaemia, mouth ulcers, and joint, eye or skin inflammation in some people. It can cause strictures (narrowing) and blockage, fistulas, abscesses and anal fissures. NIDDK notes research showing that smoking may double the chance of developing it.
Ulcerative colitis
Ulcerative colitis causes inflammation and ulcers in the inner lining of the large intestine. Typical symptoms are diarrhoea, blood or mucus in the stool, urgency, tenesmus (feeling the need to pass stool when the bowel is empty) and cramping pain. Long-standing colitis affecting a third or more of the colon increases colorectal cancer risk, so people need regular colonoscopy surveillance.
How IBS is diagnosed
NICE advises considering IBS if someone has had abdominal pain or discomfort, bloating or a change in bowel habit for at least 6 months. A diagnosis should be considered only when the pain is relieved by opening the bowels or linked to a change in stool frequency or form, plus at least 2 of:
- altered stool passage (straining, urgency, feeling of incomplete emptying);
- bloating, distension, tension or hardness of the abdomen;
- symptoms made worse by eating;
- passing mucus.
Pain from IBS can be anywhere in the abdomen and its site often varies. NICE notes this helps distinguish it from cancer-related pain, which typically stays in one place. NIDDK adds a timeframe: symptoms at least once a week in the last 3 months, starting at least 6 months ago.
Tests
- For suspected IBS (NICE): full blood count, ESR or plasma viscosity, C-reactive protein, and coeliac antibody testing (tissue transglutaminase or endomysial antibodies).
- Not routinely needed when typical IBS criteria are met (NICE): ultrasound, sigmoidoscopy or colonoscopy, barium enema, thyroid tests, stool tests for parasites, faecal occult blood and hydrogen breath tests. Practice differs between countries.
- Faecal calprotectin: a stool marker of bowel inflammation. NICE recommends it to help distinguish IBD from IBS in adults with recent-onset lower gut symptoms who are being considered for specialist referral, provided cancer is not suspected. It is also used in children with suspected IBD who have been referred.
- Faecal immunochemical test (FIT): in the UK, NICE uses FIT to guide urgent referral for suspected bowel cancer in people with symptoms such as a change in bowel habit, iron-deficiency anaemia or rectal bleeding with other features.
- Colonoscopy: used when IBD, bowel cancer or another condition needs to be ruled in or out, guided by blood and stool results, family history and symptoms.
Managing IBS
- Diet and lifestyle (NICE): regular meals without long gaps; plenty of fluid, mostly non-caffeinated; limit tea and coffee to 3 cups a day; reduce alcohol and fizzy drinks; limit fresh fruit to 3 portions a day; avoid sorbitol sweeteners if diarrhoea is a problem. Insoluble fibre such as bran is discouraged. If fibre is needed, use soluble fibre such as ispaghula or oats. Oats and up to 1 tablespoon of linseed a day may help wind and bloating.
- Further dietary advice: if symptoms persist, a low FODMAP or other exclusion diet should only be given by a professional with dietary expertise.
- Probiotics: if tried, take for at least 4 weeks and judge the effect. NICE discourages aloe vera, acupuncture and reflexology for IBS.
- Medicines by main symptom (NICE): antispasmodics as needed for pain; laxatives for constipation, but not lactulose; loperamide first for diarrhoea, adjusted to aim for a soft, formed stool; linaclotide only if several laxative classes have failed and constipation has lasted at least 12 months.
- Second line: a low-dose tricyclic antidepressant (for example amitriptyline 5 to 10 mg at night, not usually beyond 30 mg) for pain, and an SSRI only if a tricyclic has not helped. These are used for gut pain, not depression, and this use may be off-label.
- Psychological therapy: cognitive behavioural therapy, hypnotherapy or psychological therapy should be considered if symptoms persist despite medicines for 12 months.
Managing Crohn's disease and ulcerative colitis
IBD care is led by a specialist team. Treatment depends on the type of IBD, how much of the bowel is affected and how severe it is. The aim is to settle flares and then keep the disease in remission.
- Crohn's flares (NICE NG129): a conventional steroid such as prednisolone is first-line for a first flare or a single flare in 12 months. Budesonide or an aminosalicylate are weaker options when steroids are unsuitable. Exclusive liquid (enteral) nutrition is an alternative for children when growth is a concern.
- Ulcerative colitis flares (NICE NG130): for mild to moderate disease, an aminosalicylate (such as mesalazine) is first-line, given rectally for disease limited to the rectum or left side, with oral treatment and short steroid courses added if needed. Acute severe colitis needs hospital care with intravenous steroids, and a gastroenterologist and colorectal surgeon should work together.
- Keeping remission: options include aminosalicylates (mainly in ulcerative colitis) and the immunosuppressants azathioprine, mercaptopurine or methotrexate. NICE advises testing TPMT enzyme activity before azathioprine or mercaptopurine and monitoring blood counts during treatment.
- Advanced treatments: for moderate to severe disease, NICE lists biologics (infliximab, adalimumab, golimumab, vedolizumab, ustekinumab, risankizumab, mirikizumab, guselkumab) and oral small molecules (tofacitinib, filgotinib, upadacitinib, ozanimod, etrasimod) as options for specific settings. Which are available, and for which type of IBD, differs by country.
- Surgery: may be needed for narrowed segments (strictures) in Crohn's disease, or for acute severe colitis that does not respond to medicines.
- Long-term care: stopping smoking (especially important in Crohn's), bone health checks because both the disease and steroids can weaken bones, colonoscopy surveillance for colorectal cancer, and planning ahead for pregnancy with the specialist team.
Red flags / when to get urgent help
See a doctor promptly, rather than assuming IBS, if you have:
- bleeding from the rectum, or black, tarry stools;
- unintended weight loss;
- anaemia, including iron deficiency found on a blood test;
- a lump in the abdomen or rectum;
- a family history of bowel cancer, coeliac disease or IBD;
- new IBS-type symptoms at age 50 or older. NICE advises checking women and others with ovaries in this age group for ovarian cancer, because IBS rarely starts at that age. Persistent bloating, feeling full quickly, pelvic pain or urinary urgency more than 12 times a month also need testing.
Anyone with known IBD should seek same-day advice for a flare with fever, frequent bloody stools, a fast heart rate or severe pain, as these can signal a severe attack that needs hospital care. NIDDK describes more than 6 bowel movements a day, mostly with blood, as severe ulcerative colitis. Fulminant colitis (more than 10 bloody stools a day) can lead to toxic megacolon or a perforated bowel.
Frequently asked questions
Can IBS turn into IBD or cancer?
IBS causes no visible damage to the gut. New red-flag symptoms during follow-up should still prompt further tests, as NICE advises, because a different condition may have developed.
Why test calprotectin instead of going straight to colonoscopy?
Calprotectin is a simple stool test. NICE recommends it to help decide who with recent lower gut symptoms is likely to have IBD and needs specialist assessment, as long as cancer is not suspected. Red-flag symptoms still need the cancer pathway.
Should I try a low FODMAP diet on my own?
NICE advises that a low FODMAP or exclusion diet be guided by someone with dietary expertise, after general diet advice has not been enough.
Does stress cause IBD?
The causes of IBD are not fully known. NIDDK describes a combination of immune, genetic, microbiome and environmental factors. Stress can affect IBS symptoms, and stressful life events are among the factors linked with IBS.
Sources
- NICE. Irritable bowel syndrome in adults: diagnosis and management (CG61), 2008, updated 2017. nice.org.uk/guidance/cg61
- NICE. Faecal calprotectin diagnostic tests for inflammatory diseases of the bowel (HTG320, formerly DG11), 2013. nice.org.uk/guidance/htg320
- NICE. Crohn's disease: management (NG129), 2019. nice.org.uk/guidance/ng129
- NICE. Ulcerative colitis: management (NG130), 2019, with later updates. nice.org.uk/guidance/ng130
- NICE. Suspected cancer: recognition and referral (NG12), colorectal and ovarian cancer recommendations. nice.org.uk/guidance/ng12
- NIDDK. Irritable bowel syndrome: definition and facts; diagnosis. niddk.nih.gov
- NIDDK. Crohn's disease: definition and facts; symptoms and causes. niddk.nih.gov
- NIDDK. Ulcerative colitis: definition and facts; symptoms and causes. niddk.nih.gov
This article is for education and does not replace advice from a doctor, gastroenterology team or dietitian who knows the person's history.
