What is the recommended diagnostic work-up for a patient presenting with altered bowel habits, considering age, medical history, and symptoms?

Diagnostic Work-up for Altered Bowel Habits

Begin with a careful detailed history focusing on alarm features, then stratify your investigation based on age and presence of red flags—patients over 50 or those with alarm features require colonoscopy, while younger patients without red flags can be diagnosed with IBS after basic screening tests. 1

Initial Clinical Assessment

Critical Alarm Features to Identify

Screen every patient for these red flags that mandate extensive investigation:

• Unintentional weight loss — strongly suggests organic disease like inflammatory bowel disease or malignancy 2
• Rectal bleeding (beyond minor hemorrhoidal bleeding) — indicates potential colorectal cancer or IBD 1, 2
• Nocturnal diarrhea or pain that awakens the patient from sleep — suggests IBD rather than functional disorder 2
• Fever — indicates inflammatory or infectious process 2
• Anemia — suggests chronic blood loss or inflammation 1, 2
• Family history of IBD or colorectal cancer — increases pretest probability of organic disease 1

Supportive Features for Functional Bowel Disorder (IBS)

If alarm features are absent, these characteristics increase probability of IBS:

• Female sex (2:1 ratio) 2, 3
• Age under 45 years with symptom duration >2 years 1, 2, 3
• Abdominal pain relieved by defecation or associated with changes in stool frequency/consistency 2, 4
• Associated non-GI symptoms: lethargy, back pain, urinary frequency, dyspareunia 2, 3
• Comorbid fibromyalgia (present in 20-50% of IBS patients) 2, 4, 3

First-Line Screening Tests (All Patients)

Perform these basic tests regardless of clinical suspicion:

• Complete blood count — to exclude anemia 1
• Erythrocyte sedimentation rate and C-reactive protein — normal in IBS, elevated in IBD 1, 2
• Celiac serology (anti-endomysial or anti-tissue transglutaminase antibodies) — high sensitivity and specificity 1, 4
• Thyroid function tests 1
• Serum chemistries, albumin, liver function tests, calcium 1
• Stool for occult blood (fecal immunochemical test preferred) 1
• Fecal calprotectin — levels <100 μg/g support IBS diagnosis; elevated levels (>100-150 μg/g) suggest IBD inflammation 1, 2, 4
• Stool microscopy and culture — to exclude infectious causes 1

Age-Based Endoscopic Strategy

Patients Age 50 and Older

Colonoscopy is mandatory due to higher pretest probability of colorectal cancer, regardless of symptom pattern 1

Patients Under Age 50

Flexible sigmoidoscopy is sufficient if:

• No alarm features present 1
• Typical functional bowel symptoms 1
• Normal screening blood and stool tests 1

Full colonoscopy is required if:

• Any alarm features present (diarrhea, weight loss, rectal bleeding) 1
• Family history of colorectal cancer or IBD 1
• Abnormal screening tests 1

Critical Biopsy Protocol

When performing endoscopy:

• Obtain biopsies from right and left colon (not rectum) to exclude microscopic colitis, even if mucosa appears normal 1
• This is particularly important in patients with diarrhea-predominant symptoms 1

Symptom-Specific Additional Testing

For Diarrhea-Predominant Symptoms

After negative initial work-up, consider:

• Bile acid diarrhea testing with SeHCAT scan or serum 7α-hydroxy-4-cholesten-3-one — make a positive diagnosis rather than empirical treatment 1
• Lactose hydrogen breath test if patient consumes >0.5 pint (280 ml) milk daily 1 or dietary lactose withdrawal trial 1
• Stool for ova and parasites based on geographic area and travel history 1
• Laxative screen (urine for anthraquinones, bisacodyl, phenolphthalein; stool for magnesium and phosphate) if factitious diarrhea suspected 1

For Constipation-Predominant Symptoms

• Therapeutic trial of fiber is sufficient initially 1
• If symptoms persist: whole gut transit study or anorectal motility testing 1

For Pain-Predominant Symptoms

• Plain abdominal radiography during acute episode to exclude obstruction 1

Making a Positive IBS Diagnosis

You can safely diagnose IBS in primary care without extensive testing if all of the following are met:

• Age <45 years 1, 2
• No alarm features present 1, 2
• Normal physical examination 1, 3
• Basic screening tests (CBC, inflammatory markers, celiac serology, fecal calprotectin) are normal 1, 4
• Symptoms meet clinical criteria: recurrent abdominal pain with altered bowel habits, pain relieved by defecation or associated with changes in stool frequency/consistency 1, 4

Confirm diagnosis by observation over time — the incidence of new organic diagnoses after establishing functional diagnosis is extremely low 1, 3

When to Refer for Further Investigation

Refer if:

• Symptoms persist despite normal first-line investigations and treatment 1
• Atypical or severe symptoms in any age group 1
• Treatment failure after 3-6 weeks 1

Common Pitfalls to Avoid

• Do not perform colonoscopy reflexively in young patients with typical IBS symptoms and no alarm features — this leads to unnecessary procedures and increased healthcare costs 1
• Do not skip fecal calprotectin testing in patients under 40 with suspected IBS — this simple test effectively excludes IBD and avoids unnecessary endoscopy 1
• Do not forget microscopic colitis biopsies — 15% of chronic diarrhea patients have colonic pathology, with microscopic colitis being a leading diagnosis that requires histological confirmation 1
• Do not use rectal biopsies alone for microscopic colitis — right and left colon biopsies are required 1