Stool analysis

a. Occult blood. Suggests inflammation, ischemia, tumor, or various infections.

b. Leukocytes. Fecal leukocytes have a high positive predictive value for bacterial diarrhea.

c. Cultures. Indicated if history (eg, blood, travel) or stool exam (> 5 fecal leukocytes per high power field) strongly suggest a bacterial cause or if diarrhea is prolonged.

d. Ova and parasites (O&P). Fresh stool for O&P should be examined, especially when G lamblia or Cryptosporidium is suspected (eg, day-care setting).

e. pH and reducing substances. Presence of reducing substances and a low pH are indicative of malabsorption.

5. Rapid antigen tests. Enzyme-linked immunoassays for rotavirus (Rotazyme) and Giardia can be done on appropriate stool samples if clinically indicated.

6. C difficile toxin. Indicated if diarrhea is prolonged or severe and antibiotics have been given in the past 4 months (usually 4-14 days); decreased specificity in young infants

7. Fecal fat. Twenty-four- to 72-hour collection of stool for fecal fat is essential for workup of fat malabsorption.

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