What is the diagnosis, work‑up, and management for a patient with constipation‑predominant irritable bowel syndrome?

Diagnosis, Work-Up, and Management of Constipation-Predominant Irritable Bowel Syndrome

IBS-C is a positive clinical diagnosis based on Rome III criteria—recurrent abdominal pain for ≥12 weeks in the past year with at least two features: pain relief with defecation, onset associated with change in stool frequency, or onset associated with change in stool form—combined with hard stools >25% of the time and loose stools <25% of the time. 1

Diagnostic Criteria

Rome III Classification for IBS-C

• Abdominal pain is mandatory—patients with painless constipation have "functional constipation," not IBS-C. 1
• Symptoms must be present for at least 6 months before diagnosis, with criteria fulfilled for the past 3 months. 2
• Stool consistency defines the subtype: hard stools (Bristol 1-2) >25% of the time and loose stools (Bristol 6-7) <25% of the time. 1

Supportive Clinical Features

• Female sex, age <45 years, symptom duration >2 years, and frequent consultations for non-gastrointestinal complaints (lethargy, fibromyalgia, backache, urinary frequency, dyspareunia) increase diagnostic likelihood. 1
• Patients report that stress aggravates symptoms. 1
• Symptoms occur intermittently with flares lasting 2-4 days followed by remission. 1

Work-Up Algorithm

Step 1: Screen for Alarm Features

Any of the following mandates extended investigation (typically colonoscopy):

• Age ≥50 years at symptom onset 1, 3
• Unintentional weight loss 1, 3
• Rectal bleeding not attributable to hemorrhoids or anal fissures 1, 3
• Iron-deficiency anemia 1, 3
• Nocturnal diarrhea or pain that awakens the patient 1, 3
• Family history of colon cancer, inflammatory bowel disease, or celiac disease 1, 3
• Recent antibiotic use 1
• Male sex (lower threshold for investigation) 1
• Short history of symptoms 1

Step 2: Baseline Laboratory Testing (All Patients)

Perform these tests in every patient with suspected IBS-C:

• Complete blood count (CBC) to exclude anemia and inflammatory changes 1, 3, 4
• C-reactive protein (CRP) or ESR—but note that ≈20% of active Crohn's disease patients have normal CRP, so normal results do not exclude IBD. 3, 5
• Celiac serology: IgA tissue transglutaminase (IgA-tTG) plus total IgA level; if IgA-deficient, use IgG-based testing (IgG-deamidated gliadin peptide or IgG-tTG). 1, 3, 4
• Fecal calprotectin in patients <45 years with diarrhea-predominant symptoms to exclude IBD (cutoff >50 μg/g has 100% sensitivity and 97% specificity). 3, 5
• Stool testing for Giardia 1, 3
• Fecal occult blood test 1, 3

Step 3: Tests NOT Recommended

• Colonoscopy in patients <45 years with typical IBS-C symptoms and no alarm features is not cost-effective. 1, 3, 5
• Ultrasound detects incidental findings unrelated to symptoms. 3
• Hydrogen breath testing for small intestinal bacterial overgrowth is not indicated. 3
• CRP or ESR alone should not be used to screen for IBD (conditional recommendation against). 3
• Ova and parasite testing (other than Giardia) unless travel history to or recent immigration from high-risk areas. 3
• Serologic tests for IBS diagnosis have <50% sensitivity and cannot rule out IBS. 3

Step 4: When to Perform Colonoscopy

Colonoscopy is indicated when:

• Age ≥50 years (some guidelines use ≥45 years) 1, 3, 5
• Any alarm feature is present 1, 3, 5
• Family history of colorectal cancer or IBD 1, 3, 5
• Atypical or short-duration symptoms 3, 5

During colonoscopy, take biopsies from both abnormal-appearing and normal-appearing mucosa; in diarrhea-predominant patients, biopsies are essential to detect microscopic colitis even if mucosa appears normal. 3, 5

Management of IBS-C

Step 1: Patient Education and Reassurance

• Provide a clear, positive diagnosis using Rome III criteria—IBS-C is not merely a diagnosis of exclusion. 1, 3
• Explain that IBS-C is a chronic functional disorder with no increased mortality or cancer risk. 5
• Detailed explanation improves outcomes and reduces unnecessary repeat testing. 1, 3

Step 2: Dietary and Lifestyle Modifications

• Identify and eliminate common food triggers: wheat, dairy products, coffee, potatoes, corn, onions. 1, 3
• Lactose restriction only if the patient consumes >0.5 pint (≈280 mL) milk daily and has a positive lactose breath test. 1, 3
• Soluble fiber supplementation may decrease symptoms, though individual response varies. 3
• Low-FODMAP diet may reduce symptom severity. 3

Step 3: First-Line Pharmacologic Therapy

For abdominal pain:

• Antispasmodic agents (e.g., hyoscyamine, dicyclomine) 3

For constipation:

• Osmotic laxatives (polyethylene glycol) 1
• Fiber supplements (soluble fiber) 3

Step 4: FDA-Approved Prescription Therapies for IBS-C

If first-line therapies fail after 3-6 weeks, consider:

• Linaclotide 1, 6, 7
• Plecanatide 1, 8, 6, 7
• Lubiprostone 1, 6, 7
• Tenapanor 1, 7
• Tegaserod (reintroduced) 1, 6

These agents improve both constipation and abdominal pain and are generally well tolerated. 7

Step 5: Neuromodulators and Behavioral Therapy

For persistent abdominal pain or psychological symptoms:

• Tricyclic antidepressants (TCAs) 1
• Selective serotonin reuptake inhibitors (SSRIs) 1
• Brain-gut behavioral therapy 7

Step 6: Follow-Up and Reassessment

• Review patients 4-6 weeks after initiating therapy to assess response. 3
• Refer to gastroenterology if symptoms persist despite optimized first-line treatment (3-6 weeks), if atypical or severe symptoms develop, or if new alarm features appear. 3
• Reassess if the patient reaches ≥45-50 years with ongoing symptoms. 3

Common Pitfalls to Avoid

• Over-testing young patients (<45 years) with typical IBS-C symptoms—colonoscopy without alarm features delays appropriate care and is not cost-effective. 1, 3
• Serial repetitive testing increases anxiety and provides little diagnostic yield once a functional diagnosis is established. 1, 3
• Relying solely on patient-reported food intolerances without objective testing causes unnecessary dietary restrictions. 1, 3
• Assuming normal CRP excludes IBD—about 20% of active Crohn's disease patients have normal CRP. 3, 5
• Ignoring continuous pain—patients with continuous (not intermittent) pain likely have "functional abdominal pain," a severe condition requiring early recognition and different management. 1
• Fragmented specialist referrals for each new symptom increase patient burden; coordinated care is preferred. 3