Stethopedia | Approach

Approach to

Diarrhea

Assess volume status and act on severe, bloody or high-risk illness first, then sort by duration and stool type: acute infectious, C. difficile after antibiotics, or chronic watery, fatty or inflammatory.

  1. ≥3 loose stools/d: acute <14 d, chronic >4 wk
  2. Duration, blood, fever, travel, food, new drugs, antibiotics, immune status; volume status1,11
  3. Electrolytes, creatinine if more than mild; stool tests only if they change care1,2
  4. Severe, bloody or high-risk?

High risk: rehydrate and send stool tests1,11

  • Hypovolemia: orthostasis, AKI1,11
  • Fever ≥38.5 °C or >6 stools/d11
  • Sepsis: blood cultures, antibiotics1,11
  • Bloody, afebrile: no antibiotics1,5
  • Shock, ileus, megacolon: fulminant CDI3
  • Immunosuppressed, ≥70, pregnant11

→ Fulminant: PO vancomycin 500 mg QID + IV metronidazole; surgery3

If not: how long, and which type?

CausesCluesWorkupManagement

Acute infectious

  • Norovirus; traveller's E. coli
  • Campylobacter, Salmonella, Shigella
  • Shiga toxin E. coli O157 (HUS)1,5
  • Large, watery: small bowel11
  • Blood, tenesmus, fever: colonic11
  • Travel, food, sick contacts
  • None if mild and not high-risk1,2
  • Stool culture or PCR if severe1
  • Shiga toxin if bloody1
  • Oral rehydration1,2
  • Loperamide if no fever or blood1,2
  • Azithromycin: febrile dysentery, travel1

C. difficile

  • Antibiotics within 3 mo3
  • Hospital stay, age ≥65, PPI3,11
  • Fulminant colitis, megacolon
  • ≥3 unformed stools in 24 h3
  • Fever, ↑WBC, abdominal pain
  • Test only if not on laxatives3
  • Severe: WBC ≥15 ×10⁹/L3
  • Severe: Cr >133 µmol/L (1.5 mg/dL)3
  • Stop antibiotics; fidaxomicin 200 mg BID3,4,6
  • Or PO vancomycin 125 mg QID; each ×10 d3,4
  • Recurrent: fidaxomicin; FMT after 2nd3,4,7

Chronic watery

  • IBS-D, microscopic colitis
  • Drugs, bile acid; lactose, sorbitol
  • Hyperthyroidism, neuroendocrine tumour
  • Osmotic gap >125 mOsm/kg: osmotic11
  • Gap <50, persists fasting: secretory11
  • CBC, TSH, tTG, Giardia8,10
  • Calprotectin ≤40 µg/g: IBD unlikely9
  • Colonoscopy + biopsy if alarm8,11
  • Stop culprit drugs and sugars
  • Budesonide: microscopic colitis8
  • Bile acid binder for bile acid8

Chronic fatty

  • Celiac disease
  • Pancreatic insufficiency
  • Bacterial overgrowth, short bowel
  • Greasy, foul, floating stools
  • Weight loss; low iron or B12
  • tTG-IgA with total IgA8,10
  • Fecal elastase8
  • Duodenal biopsy, then gluten-free diet8
  • Pancreatic enzymes with meals11

Chronic inflammatory

  • Colorectal cancer
  • Crohn disease, ulcerative colitis
  • Ischemic, radiation, CMV colitis
  • Onset >50 y, blood, nocturnal8,11
  • Weight loss, anemia, fever
  • Stool culture, C. diff; calprotectin, CRP9,11
  • Colonoscopy with biopsies8
  • GI referral; treat IBD
  • Cancer: staging and surgery

Can't-miss cause Superscripts link to the references below.

References

  1. Shane AL, Mody RK, Crump JA, et al. 2017 Infectious Diseases Society of America clinical practice guidelines for the diagnosis and management of infectious diarrhea. Clin Infect Dis. 2017;65:e45–e80. PubMed 29053792
  2. Riddle MS, DuPont HL, Connor BA. ACG clinical guideline: diagnosis, treatment, and prevention of acute diarrheal infections in adults. Am J Gastroenterol. 2016;111:602–622. PubMed 27068718
  3. McDonald LC, Gerding DN, Johnson S, et al. Clinical practice guidelines for Clostridium difficile infection in adults and children: 2017 update by IDSA and SHEA. Clin Infect Dis. 2018;66:e1–e48. PubMed 29462280
  4. Johnson S, Lavergne V, Skinner AM, et al. Clinical practice guideline by IDSA and SHEA: 2021 focused update guidelines on management of Clostridioides difficile infection in adults. Clin Infect Dis. 2021;73:e1029–e1044. PubMed 34164674
  5. Wong CS, Jelacic S, Habeeb RL, Watkins SL, Tarr PI. The risk of the hemolytic-uremic syndrome after antibiotic treatment of Escherichia coli O157:H7 infections. N Engl J Med. 2000;342:1930–1936. PubMed 10874060
  6. Louie TJ, Miller MA, Mullane KM, et al. Fidaxomicin versus vancomycin for Clostridium difficile infection. N Engl J Med. 2011;364:422–431. PubMed 21288078
  7. van Nood E, Vrieze A, Nieuwdorp M, et al. Duodenal infusion of donor feces for recurrent Clostridium difficile. N Engl J Med. 2013;368:407–415. PubMed 23323867
  8. Arasaradnam RP, Brown S, Forbes A, et al. Guidelines for the investigation of chronic diarrhoea in adults: British Society of Gastroenterology, 3rd edition. Gut. 2018;67:1380–1399. PubMed 29653941
  9. Menees SB, Powell C, Kurlander J, et al. A meta-analysis of the utility of C-reactive protein, erythrocyte sedimentation rate, fecal calprotectin, and fecal lactoferrin to exclude IBD in adults with IBS. Am J Gastroenterol. 2015;110:444–454. PubMed 25732419
  10. Smalley W, Falck-Ytter C, Carrasco-Labra A, et al. AGA clinical practice guidelines on the laboratory evaluation of functional diarrhea and diarrhea-predominant irritable bowel syndrome in adults (IBS-D). Gastroenterology. 2019;157:851–854. PubMed 31302098
  11. Gay E, Levy N, eds. Diarrhea; C. Difficile Infection. In: Department of Medicine Housestaff Manual, 30th ed. 2024:74, 121.

For education only; not a substitute for clinical judgment or local protocols. Where sources differ, the flowchart follows the current guideline.

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