Distinguishing Irritable Bowel Syndrome (IBS) from Inflammatory Bowel Disease (IBD)

Diagnostic Approach

The American Gastroenterological Association recommends that IBS is diagnosed based on symptom criteria (Rome criteria), which include recurrent abdominal pain associated with defecation and changes in stool frequency or form 2, 3
The European Society of Gastrointestinal Endoscopy states that IBD diagnosis requires objective evidence of inflammation through laboratory testing, imaging, and endoscopy 4, 5
Alarm features that suggest IBD rather than IBS include weight loss, nocturnal symptoms, bleeding, high-volume diarrhea, fevers, and acute symptom onset, as indicated by the American College of Gastroenterology 5, 3
Age >50 years, family history of colon cancer, anemia, and rectal bleeding are red flags that warrant further investigation for IBD rather than IBS, according to the British Society of Gastroenterology [6, 7 is ignored as per instruction]

Fecal calprotectin is a crucial biomarker that helps distinguish between IBS and IBD, with levels <100 μg/g suggesting IBS is likely, 100-250 μg/g representing an intermediate range requiring clinical correlation, and >250 μg/g strongly suggesting IBD, as stated by the American Gastroenterological Association 1
C-reactive protein (CRP) is often elevated in IBD but normal in IBS, though up to 15% of IBD patients may fail to mount a CRP response, according to the European Society of Gastrointestinal Endoscopy 5, 8

Endoscopy with biopsy is essential for diagnosing IBD, showing characteristic mucosal changes and inflammation, as recommended by the American Society for Gastrointestinal Endoscopy 5, 9
IBS patients have normal endoscopic findings without evidence of inflammation, as indicated by the British Society of Gastroenterology 6

Up to 27% of IBD patients with both endoscopic and histologic healing may still experience increased stool frequency and IBS-like symptoms, according to the American Gastroenterological Association 9, 10
The Crohn's Disease Activity Index (CDAI) may be elevated in both IBS and IBD patients, highlighting the importance of objective markers of inflammation, as stated by the European Society of Gastrointestinal Endoscopy 4, 8

The American College of Gastroenterology recommends an initial symptom assessment, including evaluation for Rome criteria for IBS and screening for alarm features suggesting IBD 2, 3, 5, 6
Non-invasive testing should include measurement of fecal calprotectin and CRP, with calprotectin <100 μg/g and no alarm features suggesting IBS, and calprotectin >250 μg/g or presence of alarm features indicating referral for endoscopic evaluation, as recommended by the American Gastroenterological Association 1

Relying solely on symptoms for diagnosis without objective testing can lead to misdiagnosis, as symptoms alone cannot reliably distinguish IBS from IBD, according to the American Gastroenterological Association 4, 5
Failing to use fecal calprotectin as a screening tool before invasive testing may lead to unnecessary procedures in IBS patients or delayed diagnosis in IBD patients, as stated by the European Society of Gastrointestinal Endoscopy 1