IBS and IBD sound alike, but they are different conditions. Inflammatory bowel disease (IBD), which includes Crohn's disease and ulcerative colitis, is an immune-driven disease that inflames and can damage the bowel. Irritable bowel syndrome (IBS) is a disorder of gut–brain interaction that causes pain and changes in bowel habits without that inflammation or damage. Doctors tell them apart using blood and stool tests and, when needed, colonoscopy with biopsies.[1][2][3]
What is the difference between IBS and IBD?
The key difference is inflammation that causes damage. In IBD, the immune system drives ongoing inflammation of the gut wall, and a doctor can see it during colonoscopy and under the microscope.[6][3] In IBS, symptoms come from disordered gut–brain communication, oversensitive gut nerves and altered gut movement.[1] Researchers have found subtle immune changes in some people with IBS, but not the damaging inflammation of IBD.[1]
| IBS | IBD (Crohn's disease, ulcerative colitis) | |
|---|---|---|
| What it is | Disorder of gut–brain interaction[4] | Chronic immune-mediated inflammatory disease[2][3] |
| Cause | Gut–brain miscommunication, visceral hypersensitivity and altered motility. A previous gut infection is the best-described trigger[1] | Genetic susceptibility plus environmental factors and gut microbes, leading to a dysregulated immune response[2][3] |
| Visible inflammation | No | Yes. Crohn's is often patchy and affects the full thickness of the bowel wall. Ulcerative colitis affects the rectum and colon[6][3] |
| Typical symptoms | Abdominal pain linked to bowel movements, with changes in stool frequency or form[1] | Crohn's: abdominal pain, chronic diarrhea, weight loss, fatigue. Ulcerative colitis: bloody diarrhea[2][3] |
| Diagnosis | Symptom-based (Rome IV) with a few normal tests[4][5] | Colonoscopy and biopsies, blood tests, and often imaging[6][3] |
| Complications | Doesn't damage the bowel, though quality of life can suffer as much as with IBD[4] | Crohn's: strictures (narrowing) and penetrating disease such as fistulas, affecting about half of people within 20 years in one US population study. Ulcerative colitis: 10–20% still need surgery to remove the colon and rectum[7][3] |
| Cancer risk | Not increased[4] | Raised in long-standing ulcerative colitis[8] |
| Treatment | Diet, soluble fiber, psychological therapies and symptom-targeted medicines[4][5] | Anti-inflammatory and immune-targeted medicines, and sometimes surgery[3][6] |
How do IBS and IBD symptoms differ?
Both can cause abdominal pain and diarrhea, and the ACG notes that symptoms alone can't always tell IBS with diarrhea apart from IBD.[5] Some signs, though, point away from IBS:
- Blood in the stool. Bloody diarrhea is the usual way ulcerative colitis first shows up.[3]
- Weight loss and fatigue. Together with pain and diarrhea, these make up the typical picture of Crohn's disease, classically in a young person.[2]
- Abnormal blood results, such as micronutrient deficiencies, which are part of the assessment of Crohn's disease.[6]
Even so, IBD is uncommon in people with IBS symptoms. The ACG cites a pretest probability of under 0.5% to 1.2%, and notes that it is low when alarm features are absent.[5] If you notice any of these warning signs, see IBS red flags and talk to a doctor.
Which tests tell IBS and IBD apart?
- Fecal calprotectin is a stool test for inflammation in the bowel. The ACG suggests it (or fecal lactoferrin), together with C-reactive protein (CRP), for people with suspected IBS and diarrhea.[5] In a meta-analysis, a calprotectin of 40 µg/g or less meant a 1% or lower probability of IBD.[9]
- Blood tests such as a full blood count and CRP or ESR are part of the first assessment in UK guidelines.[4]
- Colonoscopy with biopsies confirms IBD. Characteristic findings on ileocolonoscopy (examining the colon and the end of the small intestine) and on biopsy are the standard for diagnosing Crohn's disease, and imaging is added to judge how far the disease extends.[6] Ulcerative colitis is diagnosed from clinical, laboratory, endoscopic and biopsy findings together.[3]
In IBS, these tests are expected to be normal. UK guidelines advise making a positive diagnosis of IBS when typical symptoms come with no alarm features and normal simple blood and stool tests.[4] Neither calprotectin nor CRP can confirm IBS. They only help rule IBD out.[5]
Can you have IBS and IBD at the same time?
Yes. A 2020 meta-analysis of 27 studies with 3,169 people whose IBD was in remission found that 32.5% still had symptoms meeting criteria for IBS. Even when remission was confirmed by colonoscopy or biopsy, about a quarter did. These symptoms were more common in Crohn's disease and were linked to higher anxiety and depression scores.[10]
So if you have IBD and still have symptoms, it doesn't always mean the inflammation is active. Ask your IBD team to check for active inflammation, because active IBD and IBS-type symptoms are treated differently.
How are IBS and IBD treated differently?
IBD treatment targets the inflammation. In ulcerative colitis, the goals are to bring symptoms and inflammation markers under control quickly, then keep the disease in remission with a bowel lining that looks normal on endoscopy. Medicines include 5-aminosalicylic acid drugs, corticosteroids, thiopurines, biologics and newer small-molecule drugs.[3] In Crohn's disease, treatment increasingly aims for healing of the bowel lining, not just symptom relief.[6] Surgery remains part of care for some people.[3][2]
IBS treatment targets symptoms and the gut–brain axis. Options include soluble fiber, a supervised low-FODMAP diet, gut-directed psychological therapies, peppermint oil, and medicines chosen for constipation or diarrhea.[4][5] For the full picture, see what is IBS.
How is IBS different from celiac disease?
Celiac disease is a permanent immune reaction to gluten, the protein in wheat, barley and rye. It injures the small intestine and produces specific antibodies, such as tissue transglutaminase (tTG) antibodies, that show up on blood tests. Most people need an intestinal biopsy to confirm it. Treatment is a strict gluten-free diet with lifelong medical follow-up.[11]
Celiac disease can look a lot like IBS. In a meta-analysis cited by the ACG, 3.3% of people with IBS symptoms had biopsy-proven celiac disease.[5] That's why celiac blood tests are part of the first workup.[4] Get tested before cutting out gluten, because blood tests and biopsies are not accurate once you're gluten-free.[11] A gluten-free diet isn't recommended as a treatment for IBS itself.[4]
How is IBS different from SIBO?
Small intestinal bacterial overgrowth (SIBO) means there are excessive numbers of bacteria in the small bowel, causing gut symptoms. Its symptoms, such as bloating, gas, abdominal pain and diarrhea, often masquerade as IBS.[12]
- Testing: The ACG suggests glucose or lactulose hydrogen breath tests for SIBO in people with IBS. This is a conditional recommendation based on very low-quality evidence. The other diagnostic method is culture of fluid taken from the small bowel, where 1,000 or more colony-forming units per mL suggests SIBO.[12]
- Methane is different: Excess methane on a breath test is not SIBO, because methane-producing microbes are archaea, not bacteria. The guideline calls this intestinal methanogen overgrowth.[12]
- Treatment: Antibiotics are suggested for people with symptomatic SIBO.[12] Separately, the antibiotic rifaximin is recommended for overall symptoms of IBS with diarrhea.[5]
Because SIBO's symptoms overlap so much with IBS, it can't be diagnosed from symptoms alone, and the evidence behind testing is still weak. Discuss testing with your doctor rather than relying on home kits or symptom checklists.