In a 25-year-old woman with six months of abdominal pain, non‑bloody diarrhea, weight loss, and persistent right iliac fossa pain, what is the next appropriate diagnostic step?

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Last updated: September 12, 2026 • View editorial policy

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Next Step: Fecal Calprotectin (Option B)

In this 25-year-old woman with 6 months of chronic symptoms (abdominal pain, non-bloody diarrhea, weight loss, and right iliac fossa pain), the next appropriate step is fecal calprotectin testing to screen for inflammatory bowel disease before proceeding to invasive endoscopy or advanced imaging.

Clinical Reasoning

Why Fecal Calprotectin First?

The clinical presentation strongly suggests Crohn's disease given:

  • Young age (peak incidence 15-30 years)
  • Chronic duration (>6 weeks, actually 6 months)
  • Right iliac fossa pain (terminal ileum involvement)
  • Weight loss and diarrhea
  • Non-bloody diarrhea (small bowel disease often lacks visible bleeding)

However, the ECCO-ESGAR diagnostic guidelines 1 emphasize that IBD diagnosis requires a combination of clinical, biochemical, stool, endoscopic, and imaging investigations—there is no single reference standard. The guideline explicitly states that gastrointestinal infections must be excluded and that loose stools for more than 6 weeks discriminate IBD from most infectious diarrhea 1.

The Diagnostic Algorithm

Step 1: Non-invasive screening

  • Fecal calprotectin serves as a highly sensitive biomarker to differentiate organic inflammatory disease from functional disorders
  • This avoids unnecessary invasive procedures if the test is negative
  • Stool studies should also exclude infectious causes (C. difficile, parasites, bacterial pathogens) 1

Step 2: If calprotectin is elevated

  • Proceed to ileocolonoscopy with biopsies (the gold standard per ECCO-ESGAR guidelines) 1
  • The guidelines specifically state: "For suspected IBD, ileocolonoscopy with biopsies from inflamed and uninflamed segments are required to establish diagnosis" 1

Step 3: Cross-sectional imaging

  • CT enterography or MRI enterography would follow to assess small bowel involvement, complications (strictures, fistulae), and disease extent
  • This is particularly important in Crohn's disease where transmural inflammation and extraluminal complications are common

Why Not the Other Options?

A. Sigmoidoscopy - Inadequate

  • Only visualizes the rectum and sigmoid colon
  • Will miss terminal ileal disease, which is the most likely location given right iliac fossa pain
  • The ECCO-ESGAR guidelines specify ileocolonoscopy (not sigmoidoscopy) for suspected IBD, except in acute severe colitis 1

C. CT Enterography - Premature

  • While excellent for evaluating small bowel Crohn's disease, it involves radiation exposure
  • Should be reserved for after biochemical screening and/or endoscopic evaluation
  • More appropriate for assessing disease extent and complications once IBD is confirmed

D. Small Bowel Series - Obsolete

  • Barium studies have been largely replaced by CT/MR enterography
  • Lower sensitivity and specificity
  • Does not provide tissue diagnosis

Common Pitfalls to Avoid

  1. Don't skip infection screening: Even with 6 months of symptoms, exclude C. difficile, parasites (especially Giardia), and other pathogens before labeling as IBD 1

  2. Don't assume appendicitis: While right iliac fossa pain raises this concern, the 6-month chronic course makes acute appendicitis extremely unlikely

  3. Consider iron deficiency: Check hemoglobin and ferritin—in the absence of active inflammation, ferritin <30 μg/L indicates iron deficiency; with inflammation, ferritin up to 100 μg/L may still represent iron deficiency 1

  4. Don't forget gynecologic causes: In a 25-year-old woman, consider ovarian pathology, though the chronic GI symptoms make this less likely 2

Practical Implementation

Order simultaneously:

  • Fecal calprotectin
  • Stool culture, ova and parasites, C. difficile toxin
  • CBC (anemia, leukocytosis)
  • CRP and ESR (inflammatory markers)
  • Comprehensive metabolic panel
  • Ferritin and iron studies

If fecal calprotectin is elevated (typically >50-100 μg/g depending on lab cutoffs), proceed directly to ileocolonoscopy with multiple biopsies from both inflamed and normal-appearing mucosa 1. This provides both visualization and histologic confirmation, which are essential for distinguishing Crohn's disease from ulcerative colitis and other colitides.

References

2
Research

Acute Abdominal Pain in Adults: Evaluation and Diagnosis.

American family physician, 2023

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