Acute diarrhea laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sudarshana Datta, MD [2]


Laboratory investigations performed in the evaluation of patients with acute diarrhea include spot stool analysis, detection of occult blood, white blood cells, stool culture, quantitative stool analysis, fecal weight, stool osmotic gap, fecal pH, fecal fat concentration and analysis for laxative abuse. According to the ACG guidelines, stool culture is done only in cases where the patient is at high risk of spreading the disease to others. Stool diagnostic studies are performed when symptoms last for >7 days, patient has dysentery or moderate-to-severe diarrhea and to determine etiology to enable directed pathogen-specific therapy. Antibiotic sensitivity testing for management of acute diarrhea is not advised.

Laboratory Findings

Laboratory investigations performed in the workup of patients with acute diarrhea include complete blood count, glucose levels, white blood cells (WBC) detection, urine analysis, calcium levels, Thyroid stimulating hormone (TSH) levels, complete metabolic panel and stool examination.

Laboratory Evaluation of Acute Diarrhea

Spot Stool Analysis

  • Stool spot analysis is preferred over 24 hour stool collection as it is less cumbersome.
Occult Blood
White Blood Cells
Stool Culture

Quantitative Stool Analysis

  • A 48 or 72-hour quantitative stool collection may sometimes may be useful in the evaluation of acute diarrhea in patients.
  • Full analysis includes measurement of:
Fecal Weight
  • Stool weight is also a useful index in the diagnosis of acute diarrhea.
  • Stool weight of >200g/day is considered diarrheal.
  • Low stool weight with increased frequency of stools may be indicative of incontinence or pain.
  • Cessation of diarrhea with fasting is indicative of osmotic diarrhea caused by nonabsorbable substances or secretory diarrhea due to laxatives.[6]
Stool Osmotic Gap
Fecal pH
Fecal Fat Concentration and Output
Analysis for Laxative Abuse

Stool analysis for laxatives is done in the assesment of diarrhea of unknown cause. This includes the following techniques:


  1. Viana Freitas BR, Kibune Nagasako C, Pavan CR, Silva Lorena SL, Guerrazzi F, Saddy Rodrigues Coy C; et al. (2013). "Immunochemical fecal occult blood test for detection of advanced colonic adenomas and colorectal cancer: comparison with colonoscopy results". Gastroenterol Res Pract. 2013: 384561. doi:10.1155/2013/384561. PMC 3844264. PMID 24319453.
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  5. Koontz F, Weinstock JV (1996). "The approach to stool examination for parasites". Gastroenterol Clin North Am. 25 (3): 435–49. PMID 8863034.
  6. Fordtran JS (1967). "Speculations on the pathogenesis of diarrhea". Fed Proc. 26 (5): 1405–14. PMID 6051321.
  7. 7.0 7.1 Eherer AJ, Fordtran JS (1992). "Fecal osmotic gap and pH in experimental diarrhea of various causes". Gastroenterology. 103 (2): 545–51. PMID 1634072.
  8. Bo-Linn GW, Fordtran JS (1984). "Fecal fat concentration in patients with steatorrhea". Gastroenterology. 87 (2): 319–22. PMID 6735076.
  9. Hammer HF (2010). "Pancreatic exocrine insufficiency: diagnostic evaluation and replacement therapy with pancreatic enzymes". Dig Dis. 28 (2): 339–43. doi:10.1159/000319411. PMID 20814209.
  10. Carlson J, Fernlund P, Ivarsson SA, Jakobsson I, Neiderud J, Nilsson KO; et al. (1994). "Munchausen syndrome by proxy: an unexpected cause of severe chronic diarrhoea in a child". Acta Paediatr. 83 (1): 119–21. PMID 8193462.
  11. Fine KD, Santa Ana CA, Fordtran JS (1991). "Diagnosis of magnesium-induced diarrhea". N Engl J Med. 324 (15): 1012–7. doi:10.1056/NEJM199104113241502. PMID 2005938.

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