What is the appropriate diagnostic and management approach for a patient with chronic altered bowel habits, including constipation and diarrhea, for 4 months?

Diagnostic and Management Approach for 4-Month Altered Bowel Habits

For a patient with chronic altered bowel habits (constipation and diarrhea) present for 4 months, begin immediately with screening blood tests (complete blood count, C-reactive protein, tissue transglutaminase IgA with total IgA, thyroid function) and stool tests (fecal calprotectin), then make a positive diagnosis of IBS if these are normal, while screening for alarm features that would mandate colonoscopy. 1

Initial Clinical Assessment

Obtain a detailed history focusing on specific alarm features that change management:

• Age >50 years, documented weight loss, nocturnal symptoms, rectal bleeding, family history of colon cancer, or anemia all require colonoscopy regardless of other findings 1
• Assess stool consistency patterns: hard stools >25% of time with loose stools <25% suggests IBS-constipation (IBS-C); loose stools >25% with hard stools <25% suggests IBS-diarrhea (IBS-D); both types >25% indicates IBS-mixed (IBS-M) 1
• Document if pain peaks before defecation and is relieved by defecation—this strongly supports IBS diagnosis 2
• Review all medications, surgical history (especially ileal or gastric), and recent antibiotic use 1, 3

Key behavioral features supporting IBS diagnosis include: symptoms present >6 months, frequent consultations for non-gastrointestinal symptoms, previous medically unexplained symptoms, and patient-reported stress aggravation 1

First-Line Laboratory and Stool Testing

Order these tests immediately and simultaneously: 1, 4

• Complete blood count (to exclude anemia)
• C-reactive protein and erythrocyte sedimentation rate
• Tissue transglutaminase IgA antibodies with total IgA level (to screen for celiac disease)
• Thyroid-stimulating hormone (to exclude thyroid dysfunction)
• Basic metabolic panel
• Fecal calprotectin (to exclude inflammatory bowel disease)

Critical pitfall: Fecal calprotectin <50 mg/g effectively excludes inflammatory bowel disease in patients under age 40 without alarm features 1. A level >50-60 mg/g mandates colonoscopy regardless of age 1.

Decision Point: Positive IBS Diagnosis vs. Further Investigation

If all screening tests are normal and no alarm features are present, make a positive diagnosis of IBS and initiate treatment—do not pursue further testing. 1 This approach is strongly recommended by the British Society of Gastroenterology guidelines.

If alarm features are present OR if fecal calprotectin is elevated OR if patient is >50 years old, proceed directly to colonoscopy. 1

Colonoscopy Indications and Technique

Perform colonoscopy with specific biopsy protocol when indicated: 1

• Obtain biopsies from right and left colon (NOT rectum) to exclude microscopic colitis, which presents identically to IBS but requires histologic diagnosis 1
• Microscopic colitis is a common missed diagnosis in patients with chronic diarrhea and normal-appearing mucosa 1

Secondary Evaluation if Symptoms Persist Despite Normal Initial Workup

If symptoms persist after 4-8 weeks of appropriate IBS treatment with normal initial tests, proceed with: 1

• SeHCAT testing or serum 7α-hydroxy-4-cholesten-3-one to diagnose bile acid diarrhea (present in up to 30% of IBS-D patients) 1
• Hydrogen breath testing for lactose malabsorption or small intestinal bacterial overgrowth if clinically suspected 1, 3
• Consider colonoscopy with biopsies if not yet performed 1

Important caveat: The British Society of Gastroenterology strongly recommends against empirical treatment for bile acid diarrhea without diagnostic confirmation, as this can mask other diagnoses 1.

Management Based on IBS Subtype

For IBS-C (constipation predominant): 5, 6

• Start with dietary fiber supplementation (though evidence for IBS specifically is limited) 5
• Add polyethylene glycol 3350 (17g daily dissolved in 4-8 ounces of fluid) as first-line osmotic laxative 7, 6
• If inadequate response, consider lubiprostone (prescription secretagogue) 5

For IBS-D (diarrhea predominant): 8, 5

• Loperamide 2-4mg as needed for symptom control (does not treat pain but improves stool frequency) 8, 5
• Consider probiotics, peppermint oil, or antispasmodics for pain relief 5
• If severe and refractory, alosetron may be considered (with restrictions) 5

For IBS-M (mixed pattern): 5

• Treat predominant symptom at any given time
• Antispasmodics and peppermint oil may be particularly useful as they address pain without worsening either constipation or diarrhea 5
• Low-dose tricyclic antidepressants (10-25mg amitriptyline at bedtime) can improve global IBS symptoms and pain 5

Critical Pitfalls to Avoid

• Never attribute chronic altered bowel habits to IBS without first checking celiac serology, inflammatory markers, and thyroid function 1, 4
• Do not perform celiac testing after patient has started a gluten-free diet—this causes false-negative results 9
• Do not delay colonoscopy based on young age alone when alarm features (weight loss, anemia, rectal bleeding) are present 1, 9
• Recognize that painless bowel dysfunction is NOT IBS—it is functional constipation or functional diarrhea 1
• Do not miss microscopic colitis by failing to biopsy normal-appearing mucosa during colonoscopy 1

When to Refer for Specialist Evaluation

Refer to gastroenterology if: 1

• Symptoms persist despite 8-12 weeks of appropriate treatment with normal initial workup
• Any alarm features are present
• Diagnostic uncertainty remains after initial evaluation
• Patient requires advanced testing (SeHCAT, breath testing, anorectal manometry)