What are the diagnostic criteria for Irritable Bowel Syndrome (IBS)?

Diagnostic Criteria for Irritable Bowel Syndrome

The diagnosis of IBS requires recurrent abdominal pain at least 1 day per week in the last 3 months, associated with two or more of the following: improvement with defecation, onset associated with a change in stool frequency, or onset associated with a change in stool form, with symptom onset at least 6 months before diagnosis. 1, 2

Core Diagnostic Requirements

The Rome IV criteria represent the current diagnostic standard and require all of the following 1, 2:

• Recurrent abdominal pain occurring at least 1 day per week (not just 3 days per month as in Rome III) 1, 2
• Duration: Symptoms must be present for the past 3 months, with onset at least 6 months before diagnosis 3, 4
• Two or more associated features:
  • Pain related to defecation 1, 2
  • Associated with a change in stool frequency 1, 2
  • Associated with a change in stool form/appearance 1, 2

The 6-month duration requirement is critical to distinguish IBS from transient conditions such as infections or self-limiting disorders 3, 4.

Key Clinical Features

Abdominal pain characteristics that support the diagnosis include 3:

• Pain clearly linked to bowel function (relieved by defecation or associated with changes in stool) 3
• Pain typically located in the lower abdomen 1
• Pain not necessarily related to meals 1
• Absence of structural abnormalities that could account for symptoms 3

Common supportive symptoms (not required for diagnosis but frequently present) include 3:

• Bloating or abdominal distension 3
• Abnormal stool form (hard/lumpy or loose/watery) 3
• Straining, urgency, or feeling of incomplete evacuation 3
• Passage of mucus per rectum 3
• More frequent stools at onset of pain 3

IBS Subtypes Based on Stool Pattern

Classify patients into subtypes based on predominant bowel habits 2, 5:

• IBS with diarrhea (IBS-D): Loose/watery stools ≥25% and hard/lumpy stools <25% of bowel movements 5, 6
• IBS with constipation (IBS-C): Hard/lumpy stools ≥25% and loose/watery stools <25% of bowel movements 2
• Mixed IBS (IBS-M): Both hard/lumpy stools ≥25% AND loose/watery stools ≥25% of bowel movements 2
• Unclassified IBS: Insufficient abnormality of stool consistency to meet criteria for other subtypes 2

Required Exclusion of Alarm Features

Screen for red flags that warrant further investigation before diagnosing IBS 4, 2:

• Age >50 years at symptom onset 4
• Documented unintentional weight loss 4
• Nocturnal symptoms that awaken the patient 4
• Rectal bleeding 4
• Anemia 4
• Fever 4
• Family history of colon cancer or inflammatory bowel disease 4

Appropriate Initial Workup

Baseline investigations to exclude organic disease 4:

• Complete blood count 4
• C-reactive protein or ESR 4
• Celiac serology (tissue transglutaminase antibody) 4
• Fecal calprotectin 4
• Stool examination for ova and parasites if travel history or persistent diarrhea present 4

The American College of Gastroenterology recommends that celiac disease must be excluded with serologic testing 4. If alarm features are present, consider inflammatory bowel disease and perform appropriate endoscopic evaluation 4.

Historical Diagnostic Criteria (For Context)

Manning criteria (older, less specific) included six symptoms 3, 2:

1. Pain relieved by defecation
2. More frequent stools at onset of pain
3. Looser stools at onset of pain
4. Visible abdominal distension
5. Passage of mucus per rectum
6. Sense of incomplete evacuation

The Manning criteria yield more variable prevalence estimates (2.5% to 37%) depending on how many criteria are required, whereas Rome criteria provide more consistent results 3.

Rome III criteria (superseded by Rome IV) required pain at least 3 days per month rather than 1 day per week 3. The Rome IV criteria are more restrictive, resulting in lower prevalence estimates (4.1% vs 10.1% with Rome III), and identify patients with more severe symptoms and higher psychological comorbidity 2.

Common Diagnostic Pitfalls

Do not confuse IBS with functional dyspepsia: Functional dyspepsia presents with epigastric pain that may be meal-related and is not relieved by defecation, whereas IBS pain is typically lower abdominal and related to bowel function 1. Up to 50% of patients may have overlap between these conditions 1.

Do not diagnose IBS if the 6-month duration criterion is not met: Reassess in 3-6 months, and if symptoms persist without alarm features and investigations are normal, then IBS diagnosis becomes appropriate 4.

Recognize that symptoms fluctuate over time: Subtype classification may change, and functional disorders frequently overlap with each other 2.

Note the demographic pattern: IBS symptoms peak in the third and fourth decades, with female predominance of approximately 2:1 in younger patients (20s-30s), though this bias is less apparent in older patients 3.