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Subject: Fecal Leukocytes Examination
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The presence of fecal leukocytes is an indication of an inflammatory process of the colon, including colitis caused by invasive enteric pathogens. A number of GI infections are typically associated with the presence of fecal leukocytes: Infections caused by Shigella spp., Salmonella spp., Campylobacter spp., Yersinia spp., enteroinvasive E. coli, and C. difficile, and amebic dysentery.
This test is used to detect leukocytes in stool. A fecal leukocyte examination may be indicated for patients with a clinical diarrheal syndrome and signs of colitis. A fixed smear or wet mount of diarrheal stool is stained with methylene blue and examined for the presence of PMNs using a high-power objective.
Turnaround time: <24 hours.
Stool is collected according to recommendations for stool culture and transported to the laboratory within 2 hours.
Expected results: Negative.
Negative fecal leukocyte examination does not rule out significant bacterial enteric infection.
Positive results support a diagnosis of invasive gastrointestinal infection. Enteroinvasive GI infections are usually associated with 3+ to 4+ fecal leukocytes (1–4 PMN/HPF or >5 PMN/HPF) with sensitivity >50% for specimens with results of 3+ or greater. The positive predictive value increases with increasing numbers of PMN/HPF.
Significant infections caused by a number of enteric pathogens, including Vibrio spp., enterohemorrhagic E. coli, and viral agents, do not show an increase in fecal leukocytes. An increase in fecal leukocytes is not specific for infection and may be caused by other conditions, such as inflammatory bowel disease.