One-liner#

Evaluate chronic diarrhea (>4 weeks) to distinguish functional causes (IBS-D) from organic pathology (IBD, celiac, microscopic colitis, malabsorption), using a systematic approach based on stool characteristics and alarm features.

Quick nav#

Red flags / send to ED#

Chronic diarrhea rarely requires ED referral, but send if:

  • Severe dehydration with hemodynamic instability
  • Massive GI bleeding
  • Toxic megacolon (fever, distension, severe pain in known IBD)
  • Severe electrolyte abnormalities (symptomatic hypokalemia, hyponatremia)

Alarm features (warrant expedited workup)#

  • Unintentional weight loss (>5% in 6 months)
  • Nocturnal diarrhea (wakes patient from sleep)
  • Rectal bleeding or hematochezia
  • Iron deficiency anemia
  • Age >50 with new-onset symptoms
  • Family history of IBD or colorectal cancer
  • Recent antibiotic use (C. diff can persist)
  • Fever
  • Severe abdominal pain

Key history#

Stool characteristics (guides differential):

TypeCharacteristicsSuggests
WateryHigh volume, no bloodSecretory (hormonal, bile acid) or osmotic (lactose, sorbitol)
Fatty/greasyFoul-smelling, floats, oilyMalabsorption (celiac, pancreatic insufficiency, SIBO)
InflammatoryBlood, mucus, tenesmusIBD, infection, ischemia, malignancy
Small volume, frequentUrgency, tenesmusColonic/rectal source (IBS, proctitis)

Key questions:

  • Duration and pattern: constant vs intermittent; progressive vs stable
  • Relation to meals: worse after eating (dumping, bile acid diarrhea); fasting improves (osmotic)
  • Relation to specific foods: dairy (lactose), wheat (celiac), sugar-free products (sorbitol)
  • Nocturnal symptoms: suggests organic cause (IBS typically spares sleep)
  • Fasting test: does diarrhea stop with fasting? (osmotic stops; secretory continues)

Associated symptoms:

  • Abdominal pain: crampy with defecation (IBS); severe constant (IBD flare)
  • Bloating: IBS, SIBO, lactose intolerance
  • Weight loss: malabsorption, IBD, malignancy
  • Flushing: carcinoid syndrome
  • Joint pain, skin changes: IBD, celiac
  • Anxiety/stress: IBS often stress-related

Medication and dietary review:

  • Medications causing diarrhea: metformin, colchicine, NSAIDs, PPIs, antibiotics, magnesium supplements, SSRIs, ARBs
  • Sugar alcohols: sorbitol, mannitol, xylitol (sugar-free products)
  • Excessive caffeine or alcohol
  • Artificial sweeteners
  • Recent cholecystectomy (bile acid diarrhea)

Surgical history:

  • Cholecystectomy: bile acid diarrhea (up to 10% of patients)
  • Gastric surgery: dumping syndrome
  • Small bowel resection: short bowel syndrome, bile acid malabsorption
  • Radiation: radiation enteritis

Focused exam#

  • Vitals: weight trend (compare to prior visits), orthostatic BP
  • General: nutritional status, muscle wasting, pallor
  • Abdominal: tenderness, masses, distension, surgical scars, hepatomegaly
  • Rectal: masses, blood, fissures, fistulas (Crohn’s)
  • Skin: dermatitis herpetiformis (celiac), erythema nodosum/pyoderma gangrenosum (IBD), flushing (carcinoid)
  • Thyroid: goiter (hyperthyroidism)
  • Extremities: edema (hypoalbuminemia), arthritis (IBD, celiac)
  • Perianal: fistulas, abscesses, skin tags (Crohn’s)

Differential (quick pattern recognition)#

Common/likely (outpatient)#

DiagnosisKeywords patients useKey cluesFocused exam cluesInitial next step
IBS-D“Crampy,” “urgent,” “stress makes it worse”Rome IV criteria; no alarm features; improves with defecation; no nocturnal symptomsNormal exam; mild diffuse tendernessPositive diagnosis; limited workup; dietary modification
Lactose intolerance“Bloated after milk,” “gas,” “runs right through me”Symptoms with dairy; ethnic predisposition; resolves with avoidanceNormal examLactose elimination trial; lactase supplements
Bile acid diarrhea“Watery,” “urgent,” “since gallbladder surgery”Post-cholecystectomy; watery, urgent; responds to cholestyramineNormal examEmpiric cholestyramine trial; SeHCAT if available
Medication-induced“Started after new medication”Temporal relationship; common culprits (metformin, PPIs, antibiotics)Normal examMedication review; trial discontinuation
Microscopic colitis“Watery,” “older woman,” “on lots of meds”Age >50; female; watery diarrhea; associated with NSAIDs, PPIs, SSRIsNormal examColonoscopy with random biopsies (grossly normal mucosa)
Celiac disease“Bloated,” “tired,” “runs in family”Diarrhea + bloating + fatigue; iron/B12 deficiency; family history; autoimmune diseasesMay be normal; dermatitis herpetiformisTTG-IgA + total IgA; EGD with duodenal biopsies if positive
SIBO“Bloated after eating,” “gas,” “gurgling”Post-surgical; diabetes; scleroderma; PPI use; bloating prominentDistension; hyperactive bowel soundsHydrogen breath test; empiric rifaximin trial

Can’t-miss / urgent#

DiagnosisKeywords patients useKey cluesFocused exam cluesInitial next step
IBD (Crohn’s, UC)“Bloody,” “cramping,” “losing weight,” “joint pain”Young onset; bloody diarrhea; extraintestinal manifestations; family historyAbdominal tenderness; perianal disease (Crohn’s); pallorCBC, CRP, fecal calprotectin; GI referral for colonoscopy
Colorectal cancer“Blood in stool,” “thinner stools,” “lost weight”Age >50; alarm features; family history; iron deficiency anemiaMass on rectal exam; occult blood positiveColonoscopy urgently
Chronic C. diff“Never got better after antibiotics”Prior C. diff; recurrent symptoms; ongoing antibiotic exposureMild tendernessC. diff toxin testing; oral vancomycin
Hyperthyroidism“Losing weight,” “anxious,” “heart racing”Weight loss despite good appetite; heat intolerance; tremor; palpitationsTachycardia; tremor; goiter; lid lagTSH, free T4
Chronic pancreatitis“Greasy stools,” “pain after eating,” “lost weight”Alcohol history; epigastric pain; steatorrhea; diabetesEpigastric tenderness; weight lossFecal elastase; CT or MRCP
Carcinoid syndrome“Flushing,” “wheezing,” “diarrhea”Episodic flushing; wheezing; watery diarrhea; usually with liver metastasesFlushing; hepatomegaly24-hour urine 5-HIAA; CT
VIPoma“Massive watery diarrhea,” “weak”Secretory diarrhea (>1L/day); hypokalemia; achlorhydriaDehydration; weaknessVIP level; CT

Workup#

Initial workup (all patients with chronic diarrhea):

  • CBC: anemia (bleeding, malabsorption), elevated WBC (infection, IBD)
  • CMP: electrolytes (hypokalemia), renal function, albumin (malnutrition)
  • CRP or ESR: inflammation (IBD)
  • TSH: hyperthyroidism
  • Celiac serology: TTG-IgA + total IgA (IgA deficiency causes false negative)
  • Fecal calprotectin: distinguishes inflammatory (IBD) from functional (IBS)
    • <50 μg/g: IBS very likely; IBD unlikely
    • 50–150 μg/g: gray zone; consider repeat or colonoscopy if clinical suspicion

    • 150 μg/g: suggests organic/inflammatory cause; colonoscopy indicated

Stool studies:

  • C. diff toxin: if recent antibiotics or healthcare exposure
  • Fecal fat (qualitative or 72-hour quantitative): if malabsorption suspected
  • Fecal elastase: pancreatic insufficiency (<200 μg/g abnormal)
  • Stool osmotic gap: distinguishes osmotic from secretory diarrhea
    • Osmotic gap = 290 - 2(stool Na + stool K)

    • 125: osmotic; <50: secretory

When to scope:

  • Colonoscopy with biopsies: alarm features, suspected IBD, age >45 for screening, microscopic colitis (random biopsies even if mucosa looks normal)
  • EGD with duodenal biopsies: positive celiac serology, suspected SIBO, upper GI symptoms

Specialized testing:

  • Hydrogen breath test: SIBO, lactose/fructose intolerance
  • SeHCAT scan: bile acid malabsorption (not widely available in US; empiric cholestyramine trial often used instead)
  • Gastric emptying study: if dumping syndrome suspected
  • 24-hour urine 5-HIAA: carcinoid syndrome
  • Serum chromogranin A, VIP, gastrin: neuroendocrine tumors

When NOT to do extensive workup:

  • Classic IBS-D meeting Rome IV criteria without alarm features in patient <45
  • Clear dietary trigger (lactose, sorbitol) that resolves with elimination
  • Obvious medication-induced with temporal relationship

Initial management#

  • Alarm features present: Expedited workup before empiric treatment
  • No alarm features, IBS-D pattern: Positive diagnosis; dietary modification; symptomatic treatment
  • Suspected bile acid diarrhea: Empiric cholestyramine trial
  • Suspected lactose intolerance: Elimination trial

Management by diagnosis#

IBS-D (Diarrhea-predominant IBS)#

Education:

  • IBS is a real condition involving gut-brain interaction
  • Symptoms wax and wane; goal is management, not cure
  • Dietary changes, stress management, and medications all help
  • Does NOT increase risk of cancer or IBD

Treatment:

Dietary modifications (first-line):

  • Low-FODMAP diet: effective in 50–80%; work with dietitian
  • Identify and avoid individual triggers
  • Limit caffeine, alcohol, fatty foods

Pharmacologic:

DrugDoseContraindicationsMonitoringCostNotes
Loperamide2 mg PRN or scheduled (max 16 mg/day)Bloody diarrhea; C. diffNone$First-line; use PRN or before known triggers
Rifaximin550 mg TID x 14 daysNone significantNone$$$$FDA-approved for IBS-D; can repeat if recurrence
Eluxadoline100 mg BID (75 mg if no gallbladder)No gallbladder (use 75 mg); pancreatitis; alcohol use disorderLFTs$$$$Mixed opioid agonist/antagonist
Alosetron0.5–1 mg BIDConstipation; ischemic colitis historyConstipation; ischemic symptoms$$$$Women with severe IBS-D only; restricted program
Amitriptyline10–25 mg QHS; titrate to 50–75 mgCardiac disease; glaucoma; elderlyECG if risk factors$Low-dose TCA; helps pain and slows transit
Dicyclomine10–20 mg QID PRNGlaucoma; urinary retention; elderlyAnticholinergic effects$Antispasmodic for cramping

Follow-up: 4–6 weeks after starting treatment; GI referral if refractory.

Bile acid diarrhea#

Education:

  • Bile acids not properly reabsorbed cause watery diarrhea
  • Common after gallbladder removal (up to 10% of patients)
  • Responds well to bile acid sequestrants

Treatment:

DrugDoseContraindicationsMonitoringCostNotes
Cholestyramine4 g daily–QID (start low, titrate)Bowel obstruction; triglycerides >400Triglycerides; fat-soluble vitamin levels if long-term$First-line; mix with water/juice; separate from other meds by 4 hours
Colestipol2 g daily–BIDSame as cholestyramineSame$Alternative; may be better tolerated
Colesevelam625 mg 3–6 tablets dailySameSame$$Tablet form; better tolerated; fewer drug interactions

Follow-up: 2–4 weeks; response to bile acid sequestrant is diagnostic and therapeutic.

Microscopic colitis (collagenous and lymphocytic)#

Education:

  • Inflammation visible only under microscope; colonoscopy looks normal
  • Common in older women; associated with autoimmune diseases
  • Often triggered by medications (NSAIDs, PPIs, SSRIs)
  • Usually responds well to treatment; may recur

Treatment:

Step 1: Remove triggers

  • Stop NSAIDs, PPIs, SSRIs if possible
  • Smoking cessation

Step 2: Pharmacologic

DrugDoseContraindicationsMonitoringCostNotes
Budesonide9 mg daily x 6–8 weeks, then taperActive infectionGlucose; bone density if prolonged$$$First-line; 80% response rate; high relapse when stopped
Loperamide2–4 mg PRNNoneNone$Adjunct for symptom control
Bismuth subsalicylate524 mg TID x 8 weeksAspirin allergy; renal impairmentSalicylate toxicity$Alternative for mild cases
Cholestyramine4 g daily–QIDBowel obstructionFat-soluble vitamins$If bile acid component suspected

Maintenance (if relapse):

  • Budesonide 6 mg daily or every other day
  • Consider immunomodulators (azathioprine) for refractory cases—GI to manage

Follow-up: 6–8 weeks after starting budesonide; GI follow-up for refractory or relapsing cases.

Celiac disease#

Education:

  • Autoimmune reaction to gluten (wheat, barley, rye)
  • Lifelong strict gluten-free diet is the only treatment
  • Even small amounts of gluten cause intestinal damage
  • Associated with other autoimmune conditions; screen family members

Treatment:

  • Strict gluten-free diet (GFD)—refer to dietitian experienced in celiac
  • Screen for and treat nutritional deficiencies (iron, B12, folate, vitamin D, calcium)
  • Bone density screening (increased osteoporosis risk)
  • Pneumococcal vaccination (functional hyposplenism)

Follow-up: TTG-IgA at 6 and 12 months to confirm adherence; should normalize. GI follow-up for repeat biopsy if symptoms persist despite GFD.

Small intestinal bacterial overgrowth (SIBO)#

Education:

  • Excess bacteria in small intestine causing bloating, diarrhea, malabsorption
  • Often related to anatomic abnormalities, motility disorders, or PPI use
  • May recur; address underlying cause if possible

Treatment:

DrugDoseContraindicationsMonitoringCostNotes
Rifaximin550 mg TID x 14 daysNone significantNone$$$$First-line; non-absorbed; well-tolerated
Metronidazole250 mg TID x 7–10 daysAlcohol; disulfiramGI tolerance; neuropathy if prolonged$Alternative; more side effects
Ciprofloxacin500 mg BID x 7–10 daysQT prolongation; tendinopathyTendon pain$Alternative
Amoxicillin-clavulanate875/125 mg BID x 7–10 daysPenicillin allergyGI tolerance$Alternative

Adjunctive measures:

  • Address underlying cause (stop PPI if possible, treat motility disorder)
  • Prokinetics (low-dose erythromycin) may prevent recurrence
  • Elemental diet for refractory cases

Follow-up: 2–4 weeks after treatment; if recurrent, consider maintenance antibiotics or prokinetics.

IBD (Crohn’s disease, Ulcerative colitis)#

Education:

  • Chronic inflammatory condition requiring long-term management
  • Goal is mucosal healing to prevent complications
  • Requires GI specialist co-management
  • Increased colorectal cancer risk; surveillance colonoscopy needed

PCP role:

  • Recognize and refer for diagnosis
  • Co-manage with GI: vaccinations, bone health, cancer screening
  • Monitor for medication side effects
  • Manage flares in coordination with GI

Initial management while awaiting GI:

  • Confirm diagnosis with fecal calprotectin, CRP
  • Avoid NSAIDs (can trigger flares)
  • Supportive care; antidiarrheals OK for symptom relief
  • Urgent GI referral

Medications (GI-initiated, PCP monitors):

Drug classExamplesPCP monitoring
5-ASAMesalamine, sulfasalazineRenal function annually; CBC
CorticosteroidsPrednisone, budesonideGlucose, BP, bone density, cataracts
ImmunomodulatorsAzathioprine, 6-MP, methotrexateCBC, LFTs Q3 months; TPMT before starting thiopurines
BiologicsInfliximab, adalimumab, vedolizumabTB screening before starting; infection monitoring

Follow-up: GI manages disease activity; PCP for preventive care, vaccinations (live vaccines contraindicated on immunosuppression), and monitoring for medication side effects.

Follow-up#

  • IBS-D: 4–6 weeks after starting treatment; ongoing as needed
  • Bile acid diarrhea: 2–4 weeks to assess response to sequestrant
  • Microscopic colitis: 6–8 weeks after starting budesonide
  • Celiac: 6 and 12 months for TTG-IgA; annual thereafter
  • SIBO: 2–4 weeks after treatment
  • IBD: GI co-management; PCP for preventive care

When to refer to GI:

  • Alarm features requiring colonoscopy
  • Suspected IBD
  • Positive celiac serology (for confirmatory biopsy)
  • Refractory symptoms despite initial management
  • Microscopic colitis (for diagnosis and management)
  • Recurrent SIBO

Patient instructions#

  • Keep a food and symptom diary to identify triggers.
  • Avoid foods that worsen your symptoms (common triggers: dairy, fatty foods, caffeine, alcohol, artificial sweeteners).
  • Eat smaller, more frequent meals.
  • Stay hydrated, especially if you’re having frequent loose stools.
  • Take medications as prescribed, even if you feel better.
  • Call the office if you notice blood in your stool, unintentional weight loss, fever, or worsening symptoms.
  • Follow up as scheduled to monitor your progress.

Smartphrase snippets#

.DIARRHEACHRONICIBS Chronic diarrhea meeting Rome IV criteria for IBS-D. No alarm features (no weight loss, GI bleeding, anemia, nocturnal symptoms, or family history of IBD/CRC). Fecal calprotectin normal. Plan: dietary modification (low-FODMAP trial), loperamide PRN. Discussed chronic nature and management goals.

.DIARRHEACHRONICWORKUP Chronic diarrhea with [alarm feature/diagnostic uncertainty]. Ordered [CBC, CMP, TSH, celiac serology, fecal calprotectin, colonoscopy]. Will reassess after results. Discussed importance of completing workup.

.BILEACIDDIARRHEA Chronic watery diarrhea [post-cholecystectomy/suspected bile acid malabsorption]. Plan: empiric trial of cholestyramine 4g daily, titrate as tolerated. Response to treatment is diagnostic. Discussed separating from other medications by 4 hours.

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