GI Endoscopy · 7 min read
IBD vs IBS: Calprotectin Sorts Inflammation, It Does Not Rule Out Overlap
IBS is a positive symptom diagnosis. IBD is inflammation you can measure. Patients can have both once the mucosa is quiet.
Clinical Bottom Line
| Question | Practical split |
|---|---|
| IBS | Positive diagnosis: recurrent abdominal pain related to defecation or a change in stool form or frequency (Rome IV). Normal mucosa. ACG 2021 (PMID 33315591). |
| IBD | Ulceration, chronic architectural change, transmural thickening, or a complication (stricture, fistula, bleed). Needs endoscopy plus histology at diagnosis, not a calprotectin number alone. |
| Calprotectin | A neutrophil protein. Low values make active IBD less likely and can spare colonoscopy in low-pretest adults (van Rheenen, PMID 20634346). Mid-range is not a diagnosis. High values want a look. |
| Overlap | Treated IBD with healed mucosa still gets IBS-like pain. Treat the function. Do not escalate anti-inflammatory therapy for a normal calprotectin and a normal IUS. |
| Who scopes now | Alarm features, age that makes neoplasia plausible, or a calprotectin that will not settle. Typical young IBS without alarm can stay off the table after a thoughtful stool screen. |
Does a calprotectin under 50 rule out IBD?
No. The leftover stub on this URL said a value under 50 mcg/g "decisively" excluded active IBD. van Rheenen 2010 (BMJ, PMID 20634346) is a screening meta-analysis: in adults, a low calprotectin reduced the number of people sent to colonoscopy for suspected IBD. Sensitivity is high at 50 mcg/g. It is not 100%. Timing (steroids, NSAIDs, bloody stool, sample quality) and pretest matter. Microscopic colitis and celiac disease are not calprotectin diseases. ACG 2021 (PMID 33315591) puts calprotectin or fecal lactoferrin in the IBS workup when IBD is the differential, then stops. It does not replace colonoscopy when the story is wrong.
Night stools happen in IBS. They also happen in IBD. Blood does not. Unexplained iron deficiency does not. New symptoms after 50 do not get a Rome label without a look.
What about patients who already have IBD?
Once the diagnosis is IBD, calprotectin is a monitoring tool, not a personality test. A flare workup still wants the question: is there inflammation? IUS or a flexible sigmoidoscopy can answer that without a full prep. If the mucosa and the wall are quiet, the pain may be IBS sitting on top of IBD. That is overlap, not failure of the last biologic. Do not restage SCENIC technique or UC drug choice here.
Selected references
- Lacy BE, et al. ACG Clinical Guideline: Management of Irritable Bowel Syndrome. Am J Gastroenterol. 2021;116:17-44.
- van Rheenen PF, Van de Vijver E, Fidler V. Faecal calprotectin for screening of patients with suspected inflammatory bowel disease. BMJ. 2010;341:c3369.
Last reviewed September 20, 2026. Written for clinicians triaging chronic abdominal pain and altered stool and deciding who needs a colonoscopy this month.
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