Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1350 page)

   
Expected results:
Negative.

   Limitations

   Submission of specimens >7 days after onset of acute infection is associated with decreased sensitivity. Cell culture is negative in 25% or more of patients presenting with typical EV infection. EVs may grow slowly in culture. Coxsackie A isolates grow poorly in culture; sensitivity for detection is fairly low. Commercially available RT-PCR methods have emerged as the most sensitive and specific tests for the detection of EV aseptic meningitis.

FECAL LEUKOCYTES EXAMINATION

   Definition

   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.

   Use

   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.

   Interpretation

   
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.