💡 Patients presenting with abdominal pain, altered bowel habit, or rectal bleeding require a careful and structured assessment. Causes range from benign (IBS, lactose intolerance) to life-threatening (colorectal cancer, severe IBD). History, examination, and judicious use of investigations help guide diagnosis and management.

📖 History Taking

Symptom Onset & Duration: Acute (infection, diverticulitis) vs chronic (IBS, IBD, colorectal cancer).
Nature of Bowel Habit Change: Diarrhoea, constipation, alternating pattern, urgency, nocturnal symptoms.
Associated Symptoms: Rectal bleeding, weight loss, fever, fatigue, bloating, tenesmus.
Dietary History: Lactose/gluten intake, recent travel, food poisoning risk.
Medication History: Antibiotics (C. difficile risk), opioids (constipation), laxative use.
Family History: IBD, colorectal cancer, coeliac disease.
Systemic Review: Joint pain, skin rashes (IBD), neurological symptoms, menstrual history (in women, to avoid misattribution).

🩺 Clinical Examination

General: Look for pallor (anaemia), weight loss, fever.
Abdominal exam: Tenderness (localised in diverticulitis, diffuse in gastroenteritis), masses (cancer, Crohn’s strictures), organomegaly.
Rectal exam: PR for masses, tenderness, presence of blood/mucus.
Extraintestinal signs: Aphthous ulcers, erythema nodosum, clubbing (IBD); dermatitis herpetiformis (coeliac disease).

🔬 Investigations

🧪 Bloods: FBC (anaemia, infection), CRP/ESR, LFTs, U&E, coeliac serology (anti-tTG).
💩 Stool tests: Calprotectin (inflammation vs IBS), cultures/PCR (infection), FIT test (blood in stool).
📸 Endoscopy: Colonoscopy ± biopsy (IBD, cancer, coeliac disease — small bowel biopsy).
🖥️ Imaging: CT or MRI enterography for Crohn’s; CT abdomen for diverticulitis.
🧬 Special tests: Hydrogen breath test (lactose intolerance).

📊 Causes of Abdominal Pain & Altered Bowel Habit

Cause	Diagnostic Tests	Management
🌿 Irritable Bowel Syndrome (IBS)	Rome IV criteria; stool studies to exclude inflammation; colonoscopy if red flags	Dietary modification (low FODMAP), antispasmodics, laxatives/antidiarrhoeals, probiotics, CBT
🎗️ Colorectal Cancer	FIT/gFOBT, colonoscopy with biopsy, CT for staging	Surgical resection, chemotherapy/radiotherapy (stage-dependent), long-term surveillance
🔥 Inflammatory Bowel Disease (Crohn’s, UC)	Fecal calprotectin, colonoscopy + biopsy, MRI/CT enterography	Aminosalicylates, corticosteroids, immunosuppressants, biologics, surgery if complications
📦 Diverticular Disease	CT abdomen for diverticulitis; colonoscopy for diverticulosis	High-fibre diet, antibiotics for diverticulitis, surgery if recurrent/complicated
🦠 Infectious Gastroenteritis	Stool cultures/PCR, blood tests for dehydration/electrolytes	Rehydration, antibiotics if bacterial cause confirmed, supportive treatment
💊 Medication-related	History review; exclude other pathology	Adjust/stop offending drug, probiotics for antibiotic-associated diarrhoea, laxatives for opioid constipation
🌾 Coeliac Disease	Anti-tTG antibodies; duodenal biopsy on endoscopy	Gluten-free diet for life; nutritional supplementation; follow-up for complications
🥛 Lactose Intolerance	Hydrogen breath test, elimination diet	Lactose avoidance, lactase supplements, Ca/Vit D supplementation if dairy restricted

⚠️ Red Flags (Require Urgent Referral)

Rectal bleeding in patients >50 years or with family history of colorectal cancer.
Unintentional weight loss, anorexia, night sweats.
Iron-deficiency anaemia.
Nocturnal symptoms (suggests organic disease, not IBS).
Persistent vomiting or obstructive symptoms.

🗣️ Clinical Discussion

- IBS is the most common diagnosis in young patients with chronic abdominal pain and bowel habit change, but it is a diagnosis of exclusion. - Always screen for red flags to avoid missing cancer or IBD. - Fecal calprotectin is useful to distinguish functional (IBS) from inflammatory (IBD) bowel disease. - In older adults with new bowel symptoms, assume malignancy until proven otherwise. - Clinical reasoning: • Intermittent diarrhoea, bloating, worse with certain foods → IBS or lactose intolerance. • Chronic diarrhoea, blood, weight loss, systemic features → IBD or cancer. • Acute severe abdominal pain with fever and raised WCC → diverticulitis or infection.

📚 References

NICE CG61: Management of Irritable Bowel Syndrome (2021 update)
NICE NG151: Colorectal Cancer Diagnosis & Management
British Society of Gastroenterology Guidelines on IBD (2019)
Kumar & Clark’s Clinical Medicine, 10th Ed.

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Change in Bowel habit