What is the initial management for a patient with chronic diarrhea?

Initial Management of Chronic Diarrhea

Begin with first-line laboratory and stool testing in primary care before specialist referral, while simultaneously assessing for alarm features that mandate urgent colonoscopy. 1, 2

Define the Problem First

• Confirm the patient actually has diarrhea using the Bristol Stool Chart (types 5-7), not just frequent formed stools or fecal incontinence, which patients commonly misinterpret as diarrhea 1, 2
• Verify symptoms have persisted >4 weeks, which distinguishes chronic from acute infectious causes and triggers a fundamentally different diagnostic approach 1, 2

Immediate Risk Stratification by Alarm Features

Patients with ANY of the following require urgent gastroenterology referral and colonoscopy, not conservative management: 1, 2, 3

• Age ≥45 years with new-onset symptoms
• Nocturnal diarrhea (wakes patient from sleep)
• Unintentional weight loss
• Persistent blood in stool
• Persistent fever
• Family history of inflammatory bowel disease or colorectal cancer

First-Line Investigations (Complete in Primary Care)

All patients require the following blood tests before specialist referral: 1, 2, 3

• Complete blood count (assess anemia, systemic inflammation)
• C-reactive protein and erythrocyte sedimentation rate
• Comprehensive metabolic panel (electrolytes, renal function)
• Liver function tests
• Thyroid function tests
• Iron studies, vitamin B12, folate
• Anti-tissue transglutaminase IgA with total IgA (mandatory celiac screening—commonly missed) 1, 2, 3

All patients require the following stool studies: 1, 2, 3

• Fecal calprotectin (differentiates inflammatory from non-inflammatory causes)
• Fecal immunochemical test (FIT) for occult blood
• Stool culture if infectious etiology suspected based on recent travel, antibiotic use, or outbreak exposure

Age-Stratified Endoscopic Approach

For patients ≥45 years: Full colonoscopy with random biopsies from right and left colon is mandatory, even if mucosa appears normal, to exclude colorectal cancer and microscopic colitis 1, 2, 3

For patients <40 years without alarm features and normal fecal calprotectin: Flexible sigmoidoscopy with biopsies may suffice, or consider positive diagnosis of irritable bowel syndrome using Rome IV criteria after completing basic screening 1, 2, 3

Critical Pitfall: Never Skip Biopsies

Obtain biopsies from both right and left colon even when mucosa appears completely normal endoscopically, as microscopic colitis has entirely normal-appearing mucosa but shows characteristic histologic changes that are the only way to make this diagnosis 2, 3

Symptomatic Management While Awaiting Results

Loperamide is first-line antidiarrheal therapy: 2, 3, 4

• Initial dose: 4 mg (two capsules) followed by 2 mg after each unformed stool
• Maximum daily dose: 16 mg (eight capsules)
• Average maintenance dose: 4-8 mg daily
• Clinical improvement usually observed within 48 hours

Supportive measures: 1, 2

• Maintain adequate oral hydration with oral rehydration solutions if volume depleted
• Dietary modifications if specific aggravating foods identified
• Instruct patients to record stool frequency and report fever or orthostatic symptoms

Secondary Testing if Initial Workup Negative

Test for bile acid diarrhea with objective testing (SeHCAT or serum 7α-hydroxy-4-cholesten-3-one), not empiric trial, especially if patient has risk factors including ileal resection, cholecystectomy, or pelvic radiotherapy 1, 2, 3

Common Diagnostic Pitfalls to Avoid

• Missing microscopic colitis by performing colonoscopy without biopsies or relying on CT imaging alone, which cannot detect this diagnosis 2, 3
• Premature IBS diagnosis using Rome IV criteria alone without completing basic blood and stool screening first (Rome criteria have only 52-74% specificity) 3
• Missing celiac disease by forgetting anti-tissue transglutaminase IgA screening 1, 2, 3
• Inadequate colonoscopy in older patients leading to missed colorectal cancer—reduction of missed diagnoses to <1% is the audit standard 1
• Assuming normal CT excludes significant pathology—CT is inadequate for detecting microscopic colitis, early inflammatory bowel disease, or subtle mucosal abnormalities 3