Confusable diagnoses · PANCE / PANRE

Irritable Bowel Syndrome vs Celiac Disease

Written & clinically reviewed by Ryan Busch, PA-C · Updated August 2026 · Report an error

Irritable Bowel Syndrome and Celiac Disease are easy to mix up on the boards. Here's a side-by-side comparison — presentation, workup, imaging, and first-line treatment — drawn from our full outlines.

Irritable Bowel Syndrome vs Celiac Disease at a glance

  • Irritable Bowel Syndrome: Disorder of gut-brain interaction with recurrent abdominal pain and altered bowel habits without structural disease.
  • Celiac Disease: Immune-mediated small bowel injury triggered by dietary gluten in genetically susceptible (HLA-DQ2/DQ8) individuals.

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Question 1GastrointestinalMedium
A 22-year-old woman presents with diffuse abdominal bloating, cramping, and alternating diarrhea and constipation for 8 months. Symptoms are worse during stress and partially relieved by defecation. She has no nocturnal symptoms, weight loss, or blood in stool. CBC, CMP, TSH, and CRP are normal. Colonoscopy 6 months ago was normal. Which of the following is the most likely diagnosis?
  • ABile acid malabsorption
  • BIrritable bowel syndrome
  • CFunctional dyspepsia
  • DCeliac disease
Reveal answer & full explanation
Correct answer: B — Irritable bowel syndrome
  • ABile acid malabsorption
  • BIrritable bowel syndrome✓
  • CFunctional dyspepsia
  • DCeliac disease

Why Irritable bowel syndrome is correct

  • This presentation is classic irritable bowel syndrome (IBS) per Rome IV criteria: recurrent abdominal pain at least 1 day/week for 3 months, associated with defecation, change in stool frequency or consistency.
  • No alarm features are present (no nocturnal symptoms, weight loss, blood in stool, or elevated inflammatory markers).
  • Normal colonoscopy rules out inflammatory bowel disease (IBD).

Why the others are wrong

  • Bile acid malabsorption — causes painless or urgency-predominant watery diarrhea, typically after ileal resection, cholecystectomy, or Crohn disease, and does not produce the alternating constipation or the stress-triggered pain relieved by defecation described here.
  • Celiac disease — Celiac serology is reasonable to check, but the overall presentation fits IBS.
  • Functional dyspepsia — Functional dyspepsia is centered on upper GI symptoms (epigastric pain, early satiety), not the diffuse cramping and altered bowel habits described here.

Additional high-yield points

  • First-line management includes reassurance, dietary modification (low-FODMAP diet), soluble fiber for constipation-predominant IBS, and antispasmodics for pain.
Question 2GastrointestinalMedium
A 35-year-old female has 3 years of chronic watery diarrhea (6-8 stools/day), 15 lb weight loss, and fatigue. Anti-tissue transglutaminase (anti-tTG) IgA is 12x upper limit of normal (ULN) and endomysial antibody (EMA) IgA is positive. Total serum IgA is normal. Duodenal biopsy shows Marsh 3b villous atrophy. Which of the following is the most appropriate long-term treatment?
  • ALactose-restricted diet
  • BLow-FODMAP diet
  • CStrict gluten-free diet
  • DBudesonide
Reveal answer & full explanation
Correct answer: C — Strict gluten-free diet
  • ALactose-restricted diet
  • BLow-FODMAP diet
  • CStrict gluten-free diet✓
  • DBudesonide

Why Strict gluten-free diet is correct

  • Celiac disease is an autoimmune enteropathy triggered by gliadin proteins, and the only effective treatment is a strict lifelong gluten-free diet (GFD)
  • This patient has highly positive anti-tissue transglutaminase (anti-tTG) IgA (12x ULN), positive endomysial antibody (EMA) IgA, and Marsh 3b villous atrophy on biopsy — all confirming celiac disease
  • Total IgA was checked and is normal, ruling out IgA deficiency (present in 2-3% of celiac patients) that would cause false-negative serology

Why the others are wrong

  • Lactose-restricted diet — addresses secondary lactase deficiency that can accompany celiac disease but does not treat the underlying autoimmune enteropathy; at most an adjunct (right-concept-wrong-target)
  • Low-FODMAP diet — used for irritable bowel syndrome; does not address celiac pathophysiology or halt villous atrophy (confused-with IBS)
  • Budesonide — a corticosteroid used for refractory celiac disease (persistent villous atrophy after strict GFD for over 12 months); not first-line at diagnosis (right-concept-wrong-stage)

Additional high-yield points

  • Serology: anti-tTG IgA has sensitivity 95%, specificity 98%; EMA IgA is highly specific
  • Biopsy: Marsh 3 = villous atrophy, crypt hyperplasia, intraepithelial lymphocytes above 25/100 enterocytes
  • Monitoring: anti-tTG IgA titers normalize within 6-12 months on GFD
  • Replace nutritional deficiencies: iron, folate, vitamin D, calcium, B12, zinc
  • Refractory celiac: persistent villous atrophy after strict GFD for over 12 months
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Side-by-side comparison

FeatureIrritable Bowel SyndromeCeliac Disease
At a glanceDisorder of gut-brain interaction with recurrent abdominal pain and altered bowel habits without structural disease.Immune-mediated small bowel injury triggered by dietary gluten in genetically susceptible (HLA-DQ2/DQ8) individuals.
Classic presentationYoung woman with chronic abdominal pain relieved by defecation, alternating bowel habit, and bloating — exam normal.; Recurrent abdominal pain related to defecation (relief or worsening); Change in stool frequency or form; Bloating, distension; Mucus in stool; Symptoms worsened by stress and certain foods (FODMAPs); Sensation of…Iron-deficiency anemia or osteoporosis in an adult without obvious cause — test for celiac disease.; Classic/GI: chronic diarrhea, steatorrhea, abdominal pain, bloating, flatulence, weight loss; Non-classic/atypical: iron-deficiency anemia (most common adult presentation), osteoporosis, infertility, recurrent miscarriage, neurologic…
Workup / key labsRome IV: Recurrent abdominal pain on average ≥1 day/week in the last 3 months, associated with ≥2 of: (1) related to defecation, (2) change in stool frequency, (3) change in stool form. Symptom onset ≥6 months prior to diagnosis. Subtypes by predominant stool form using Bristol Stool Scale: IBS-C, IBS-D, IBS-M, IBS-U.; CBC (exclude…Adults: positive serology (tTG IgA with normal total IgA, or EMA, or DGP) + duodenal biopsy showing Marsh II-IV changes on a gluten-containing diet + clinical response to GFD. Children (ESPGHAN 2020): non-biopsy diagnosis allowed if tTG IgA ≥10× ULN (with normal total IgA) + positive EMA IgA on a second blood sample; HLA typing and…
ImagingColonoscopy — NOT routinely required for typical IBS without alarm features; perform if age ≥45 (CRC screening), alarm features, family history of IBD/CRC, or refractory symptoms; Random colonic biopsies if chronic watery diarrhea (microscopic colitis)Upper endoscopy with multiple duodenal biopsies — REQUIRED for diagnosis in adults: 1-2 from bulb + ≥4 from second/third portion; findings: scalloping of folds, mosaic pattern, decreased folds; Histology: increased intraepithelial lymphocytes (>25 per 100 enterocytes), crypt hyperplasia, villous atrophy (Marsh classification 0-IV);…
First-line treatmentEstablish therapeutic relationship; educate that IBS is a real, chronic, manageable condition; Dietary modification: regular meals, adequate fiber (soluble — psyllium); trial of low-FODMAP diet under dietitian guidance; Exercise, sleep hygiene, stress management; Cognitive behavioral therapy and gut-directed hypnotherapy (strong evidence)STRICT LIFELONG GLUTEN-FREE DIET — only proven treatment; Avoid wheat, rye, barley, malt; oats often tolerated (must be uncontaminated); Referral to registered dietitian experienced in celiac disease; Treat nutritional deficiencies: iron, B12, folate, vitamin D, calcium, zinc; DEXA scan at diagnosis; supplement vitamin D and calcium;…

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Full outlines

Irritable Bowel Syndrome (IBS) Celiac Disease All 514 diagnoses

Educational use only. This outline is a study aid for PA students and is not medical advice or a substitute for clinical judgment. FirstPassPA is an independent study tool and is not affiliated with, endorsed by, or sponsored by NCCPA or PAEA. PANCE® and PANRE® are registered trademarks of the National Commission on Certification of Physician Assistants; End of Rotation™ is a program of the Physician Assistant Education Association.