What are the diagnostic criteria for IBS-C (Irritable Bowel Syndrome with Constipation)?

Diagnosing IBS-C (Irritable Bowel Syndrome with Constipation)

IBS-C is diagnosed using the Rome II criteria: at least 12 weeks (need not be consecutive) in the preceding 12 months of abdominal discomfort or pain that has 2 of 3 features: (1) relieved with defecation, (2) onset associated with a change in frequency of stool, and/or (3) onset associated with a change in form of stool, combined with hard/lumpy stools and fewer than 3 bowel movements per week. 1

Core Diagnostic Criteria

The diagnosis is symptom-based and positive, not a diagnosis of exclusion. 1

Rome II Criteria Requirements 1

The patient must have at least 12 weeks of abdominal discomfort or pain (weeks need not be consecutive) in the preceding 12 months, with 2 of the following 3 features:

• Pain relieved with defecation 1
• Onset associated with a change in frequency of stool 1
• Onset associated with a change in form (appearance) of stool 1

Constipation-Specific Features 1

For IBS-C specifically, supportive symptoms include:

• Abnormal stool frequency (fewer than 3 bowel movements per week) 1
• Abnormal stool form (lumpy/hard stool) 1
• Abnormal stool passage (straining or feeling of incomplete evacuation) 1
• Passage of mucus 1
• Bloating or feeling of abdominal distention 1

Clinical Assessment Algorithm

Step 1: Establish Positive Symptoms 1

A working diagnosis can be safely made in general practice based on:

• Typical symptoms meeting Rome criteria 1
• Normal physical examination 1
• Absence of alarm features (weight loss, rectal bleeding, nocturnal symptoms, or anemia) 1

Step 2: Identify Supportive Features 1

The diagnosis is more likely if the patient is:

• Female 1
• Aged <45 years 1
• Symptom duration >2 years 1
• History of frequent attendance with non-gastrointestinal symptoms 1

Step 3: Screen for Alarm Features 1

Perform screening tests to exclude organic disease:

• Complete blood count (to detect anemia) 1
• Stool Hemoccult test 1
• Erythrocyte sedimentation rate (particularly in younger patients) 1

Red flags requiring further investigation include:

• Fever 1
• Weight loss 1
• Blood in stools 1
• Anemia 1
• Nocturnal symptoms 1
• Abnormal physical findings 1

When to Perform Additional Testing

Age-Based Colonoscopy Recommendations 1

• Patients over age 50 years: Colonoscopy is recommended due to higher pretest probability of colorectal cancer 1
• Patients over age 45 years at symptom onset: Consider colonoscopy, particularly with family history of colon cancer 1

Selective Additional Testing 1

If symptoms are atypical, history is short, or patient is over 45, perform:

• Sigmoidoscopy (if colonic symptoms present; biopsy any abnormality and all patients with diarrhea to detect microscopic colitis) 1
• Thyroid function tests (yields 1-2% abnormalities) 1
• Antiendomysial antibodies (to exclude celiac disease; yields 1-2% abnormalities) 1
• Stool microscopy (for ova and parasites, particularly with predominant diarrhea or endemic infection areas) 1
• Urinary screen for laxatives (yields 1-2% abnormalities) 1

Lactose Testing 1

Lactose tolerance testing is only indicated if the patient consumes substantial amounts of milk (>0.5 pint/280 ml per day), as it reveals lactose malabsorption in 8-25% of cases but rarely cures IBS. 1

Common Pitfalls to Avoid

Do Not Over-Investigate 1

• Avoid repetitive, anxiety-provoking serial testing if initial screening is negative 1
• The diagnosis should be confirmed in general practice by observation over time, not by exhaustive testing 1

Do Not Ignore Non-Gastrointestinal Symptoms 1

Non-gastrointestinal symptoms are supportive of IBS diagnosis and include:

• Lethargy and poor sleep 1
• Fibromyalgia 1
• Backache 1
• Urinary frequency 1
• Dyspareunia 1

Recognize Psychosocial Factors 1

Psychological stress and psychosocial factors may exacerbate symptoms and should be identified, particularly:

• History of major life stress (abuse, family death, divorce) 1
• Comorbid psychiatric disorders 1
• Maladaptive coping style 1

These factors strongly influence clinical outcome and may require psychological or psychopharmacological treatment. 1

Prognosis and Follow-Up 1

Once a functional diagnosis is established, the incidence of new non-functional diagnoses is extremely low. 1 The diagnosis presumes the absence of structural or biochemical explanation for symptoms. 1