Approach to Chronic Diarrhoea
Begin with a detailed history focusing on alarm features (blood in stool, unintentional weight loss, nocturnal symptoms, fever, age >45 years), followed by first-line laboratory testing including complete blood count, C-reactive protein, IgA tissue transglutaminase with total IgA, and stool testing for Giardia antigen. 1
Definition and Initial Risk Stratification
Chronic diarrhoea is defined as the abnormal passage of ≥3 loose or liquid stools per day for more than 4 weeks, and/or stool volume >200 g/day. 2, 1 This duration distinguishes it from acute infectious causes that are typically self-limiting. 3
Key historical elements to elicit:
Alarm features requiring urgent evaluation: Blood in stool, unintentional weight loss, nocturnal diarrhoea (suggests organic disease rather than functional), fever, symptoms <3 months duration, age >45 years with new-onset symptoms. 1, 3 These features mandate prompt gastroenterology referral and endoscopic evaluation. 4
Surgical history: Terminal ileal resection, cholecystectomy, or abdominal radiotherapy are strong risk factors for bile acid diarrhoea. 1 Post-surgical patients may also develop bacterial overgrowth, particularly after procedures creating blind loops (Billroth II, Roux-en-Y) or loss of the ileocaecal valve. 2
Stool characteristics: Bulky, pale, malodorous stools suggest malabsorption/steatorrhea, while liquid stools with blood or mucus suggest colonic/inflammatory etiology. 3 Patients often focus on consistency rather than frequency. 2
Medication review: Proton pump inhibitors, antibiotics, metformin, and laxatives are common culprits. 1 This is a frequently overlooked cause. 1
First-Line Laboratory Testing (Complete in Primary Care)
All patients with chronic diarrhoea require the following baseline investigations: 1
Coeliac disease screening: IgA tissue transglutaminase (tTG) plus total IgA level to detect IgA deficiency (which causes false-negative IgA-tTG results). 1 This has sensitivity and specificity exceeding 90% when using thresholds of 7-15 AU/mL. 1 This must be done in all patients regardless of symptom presentation. 1
Giardia testing: Giardia antigen test or PCR (sensitivity and specificity >95%). 1 This is mandatory screening, not reserved for travel history. 1
Inflammatory markers: Complete blood count, C-reactive protein, comprehensive metabolic panel, liver function tests, iron studies, vitamin B12, folate. 1, 3
Stool studies: Fecal calprotectin (to screen for inflammatory conditions), fecal immunochemical test (FIT) for occult blood. 1, 3 Elevated calprotectin (>900) indicates significant colonic inflammation and organic pathology. 3
Thyroid function tests to exclude hyperthyroidism. 3
Common pitfall: Ordering broad ova and parasite panels in patients without travel history has extremely low yield. 1 Focus on Giardia specifically. 1
Age-Stratified Endoscopic Evaluation
Patients ≥45 Years Old
More than 90% of patients with chronic diarrhoea over 45 years should undergo colonoscopy due to the frequency and clinical significance of colonic neoplasia in older subjects. 2, 3 This is a quality benchmark. 2
Colonoscopy technique: Aim for >90% caecal intubation rate with terminal ileal intubation in >70% of cases if clinically necessary. 2, 3
Biopsy protocol: Obtain biopsies from both right and left colon (not rectum) even if the mucosa appears completely normal, as microscopic colitis has entirely normal-appearing mucosa on endoscopy but shows characteristic histologic changes. 2, 3 This is essential to avoid missing microscopic colitis. 3
Patients <45 Years Old
Patients under 40 years without alarm features and normal fecal calprotectin should avoid immediate colonoscopy and can be managed with positive diagnosis of irritable bowel syndrome using Rome IV criteria after basic screening. 3 However, minimizing inappropriate first-line investigations (such as barium enema) in this age group is a quality goal. 2
If alarm features are present or inflammatory markers are elevated, proceed with colonoscopy regardless of age. 1
Evaluation for Specific Treatable Causes
Bile Acid Diarrhoea
SeHCAT testing is the preferred diagnostic test for bile acid diarrhoea in patients with risk factors (terminal ileal resection, cholecystectomy, radiotherapy). 1 Where SeHCAT is unavailable, serum C4 (7α-hydroxy-4-cholesten-3-one) assay can be used as an alternative. 1
Common pitfall: Overlooking bile acid diarrhoea in patients with prior cholecystectomy or ileal resection. 1 While empiric trial of bile acid sequestrants may be considered when testing is unavailable, formal diagnosis is preferred. 1
Microscopic Colitis
Microscopic colitis requires colonoscopy with biopsies and cannot be diagnosed without histology. 3 It is a secretory diarrhoea affecting older persons and can present similarly to irritable bowel syndrome but requires different treatment. 5
Small Bowel Bacterial Overgrowth
An empirical trial of antibiotics is recommended rather than routine hydrogen or methane breath testing. 1 This is particularly relevant in post-surgical patients with blind loops or loss of the ileocaecal valve. 2
Coeliac Disease
If coeliac serology is positive, upper endoscopy with duodenal biopsies must be performed to confirm the diagnosis. 1 Treatment requires a strict gluten-free diet. 1
Common Diagnostic Pitfalls to Avoid
Assuming functional diarrhoea based on Rome IV criteria alone: These criteria have only 52-74% specificity and do not reliably exclude IBD, microscopic colitis, or bile acid diarrhoea. 1, 3 Complete basic screening first. 3
Missing IgA deficiency when interpreting coeliac serology: This causes false-negative IgA-tTG results. 1 Always order total IgA alongside IgA-tTG. 1
Relying on CT imaging alone: CT is inadequate for detecting microscopic colitis, early inflammatory bowel disease, or subtle mucosal abnormalities that are only visible endoscopically with histology. 3 Normal CT does not exclude significant colonic pathology. 3
Failing to obtain colonic biopsies: Even with normal-appearing mucosa, biopsies are essential to diagnose microscopic colitis. 2, 3
Neglecting medication review: This is a common and easily reversible cause. 1
Premature IBS diagnosis: Reduction of missed diagnoses of inflammatory bowel disease should be <10%, and missed colorectal cancer <1%. 2 These quality benchmarks require thorough investigation before labeling symptoms as functional.
Categorization and Targeted Management
Once serious pathology is excluded, chronic diarrhoea can be categorized into three main types: watery (functional, secretory, osmotic), fatty (malabsorption), and inflammatory. 1, 5
Specific treatments based on identified causes:
Bile acid diarrhoea: Cholestyramine as initial therapy, with alternate bile acid sequestrants when tolerability is an issue. 1
Coeliac disease: Strict gluten-free diet. 1
Inflammatory bowel disease: Disease-modifying therapies based on type and severity. 1
Lactose intolerance: Dietary lactose restriction or lactase enzyme supplements. 1
Medication-induced: Discontinuation of offending agents when possible. 1
Symptomatic management when specific cause cannot be identified or treated:
Loperamide is first-line antidiarrheal: initial dose 4 mg followed by 2 mg after each unformed stool, average maintenance dose 4-8 mg daily. 3
Dietary modifications: Eliminate potential triggers such as caffeine, alcohol, sorbitol, and fructose. 1
Special Considerations
Faecal impaction with overflow diarrhoea should be considered especially in the elderly, those with cognitive or behavioral issues, learning difficulties, or neurological/spinal disease. 2 Clinical judgment rather than marker studies is recommended to confirm this. 2 A focused baseline assessment should include anorectal examination. 2
For patients with persistent faecal incontinence, anorecal manometry and endoanal ultrasonography are recommended once conservative measures have been exhausted and surgical intervention is contemplated. 2