Diarrhea Guidelines

Updated: Jan 31, 2020
  • Author: Stefano Guandalini, MD, AGAF; Chief Editor: Carmen Cuffari, MD  more...
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Guidelines Summary

British Society of Gastroenterology guidelines for the investigation of chronic diarrhoea in adults  [35]

Clinical assessment

  • Recommend a careful detailed history to plan investigations.
  • Recommend screening blood tests for the exclusion of anemia, celiac disease, etc, as well as stool tests for inflammation.
  • Recommend making a positive diagnosis of irritable bowel syndrome (IBS) following basic blood and stool screening tests.

Cancer or inflammation

  • Recommend excluding colorectal cancer in those with altered bowel habit ± rectal bleeding by colonoscopy.
  • Suggest use of testing for fecal blood loss by fecal immunochemical testing in primary or secondary care, either as an exclusion test or to guide priority of investigations in those with lower gastrointestinal symptoms (chronic diarrhea) but without rectal bleeding.
  • Fecal calprotectin is recommended to exclude colonic inflammation in those suspected with IBS and under the age of 40.

Secondary clinical assessment

  • If symptoms persist despite normal first-line investigations and treatment, then referral for further investigations is recommended.
  • We recommend blood and stool tests to exclude malabsorption and common infections (especially in the immunocompromised or elderly).

Common disorders

  • In those with functional bowel or IBS-diarrhea, a positive diagnosis of bile acid diarrhea should be made either by selenium-75-homocholic acid taurine ( 75SeHCAT) testing or serum bile acid precursor 7α-hydroxy-4-cholesten-3-one (7αHCO, or 7αC4) (depending on local availability).
  • Recommend colonoscopy with biopsies of the right and left colon (not rectal) to exclude microscopic colitis.


  • If lactose maldigestion is suspected, suggest hydrogen breath testing (if available) or withdrawal of dietary lactose/carbohydrates from the diet.
  • Magnetic resonance (MR) enterography (MRE) is recommended for evaluation of small bowel abnormalities depending on availability.
  • Video capsule endoscopy (VCE) is recommended for assessing small bowel abnormalities depending on local availability.
  • We do not recommend small bowel barium follow through or barium enteroclysis for the evaluation of small bowel abnormalities because of its poor sensitivity and specificity.
  • Recommend enteroscopy only for targeted lesions identified by MRE or VCE and not for diagnosis of chronic diarrhea.
  • Recommend fecal elastase testing when fat malabsorption is suspected. We do not recommend para-aminobenzoic acid (PABA) testing.
  • MR imaging (MRI) (rather than computed tomography (CT)) is recommended for assessing structural anomalies of the pancreas in suspected chronic pancreatitis.
  • If small bowel bacterial overgrowth is suspected, we recommend an empirical trial of antibiotics, as there is insufficient evidence to recommend routine hydrogen or methane breath testing.

Surgical and structural disorders

  • We recommend use of anorectal manometry and endoanal ultrasound only when other local pathology has been excluded and conservative measures exhausted.
  • Recommend radiologic modalities for the investigation of fistulae—MRI or CT with contrast follow through.

Rare causes

  • Diarrhea due to hormone secreting tumors is rare; hence, we recommend testing only when other causes of diarrhea have been excluded.

Canadian Association of Gastroenterology (CAG) diagnostic and treatment guidelines for bile acid diarrhea (BAD)

The Canadian Association of Gastroenterology (CAG) has issued guidelines on the diagnosis and treatment of bile acid diarrhea (BAD). [37]

Diagnosis of bile acid diarrhea

In patients with chronic nonbloody diarrhea, the initial assessment for suspected bile acid diarrhea (BAD) should be based on risk factors (history of cholecystectomy, terminal ileal resection, radiotherapy) rather than symptoms.

In patients with chronic diarrhea, including diarrhea-predominant irritable bowel syndrome (IBS-D) and functional diarrhea, 75selenium homocholic acid taurine (SeHCAT) testing or 7α-hydroxy-4-cholesten-3-one (C4) assay is recommended to evaluate for BAD. SeHCAT testing is also recommended in patients with persistent diarrhea who have Crohn disease of the small intestine without objective evidence of inflammation. The guidelines do not take a position for or against the use of fibroblast growth factor 19 (FGF19) assay for BAD diagnosis.

In patients with suspected BAD, SeHCAT testing is preferred over initiation of empiric bile acid sequestrant therapy (BAST) to establish diagnosis.

Induction therapy for bile acid diarrhea

In patients with type 1 or type 3 BAD, any remediable causes (eg, Crohn disease, microscopic colitis, small intestinal bacterial overgrowth [SIBO]) should be treated along with BAD to induce a clinical response.

In patients with BAD, cholestyramine treatment is preferred over no treatment to induce a clinical response. Cholestyramine is preferred over other BASTs as initial therapy except in patients who cannot tolerate cholestyramine.

In patients who are receiving empiric BAST, the daily dose should be gradually titrated to minimize adverse effects.

BAST is discouraged in patients with Crohn disease with extensive ileal involvement or resection.

Patients with BAD who have recurrent or worsening symptoms despite stable BAST therapy should be re-evaluated diagnostically.

Concurrent medications should be reviewed in patients being considered for BAST therapy to minimize the possibility of drug interactions.

Maintenance treatment for bile acid diarrhea

In patients with BAD in whom BAST elicits a response, a trial of intermittent on-demand dosing is recommended.

Patients who are unable to tolerate BAST should receive alternative antidiarrheal agents instead of no treatment to alleviate long-term symptoms.

Empiric BAST being given as maintenance therapy should be administered at the lowest dose necessary to minimize symptoms. The guidelines do not take a position on whether to recommend for or against measuring fat-soluble vitamin levels at baseline and annually thereafter.