WBC 2-5 per High Power Field in Fecal Analysis
A finding of 2-5 white blood cells per high power field (WBC/HPF) in fecal analysis indicates mild intestinal inflammation, but this result has limited clinical utility and should not be used alone to guide diagnosis or treatment decisions. 1
Clinical Significance and Interpretation
The presence of fecal leukocytes suggests inflammatory diarrhea, but this distinction performs poorly in establishing the infectious cause of diarrhea, particularly among hospitalized patients. 1 The finding of 2-5 WBC/HPF falls into a gray zone:
Diagnostic thresholds vary in the literature: Studies have used cutoffs ranging from >1 WBC/HPF to >5 WBC/HPF, with higher thresholds generally improving specificity at the cost of sensitivity. 2, 3
In bacterial gastroenteritis: A threshold of >5 WBC/HPF demonstrated a positive likelihood ratio of 4.56 and negative likelihood ratio of 0.32 in developed countries, but only 2.94 and 0.6 respectively in resource-poor settings. 4
For shigellosis specifically: The presence of >50 WBC/HPF had only modest sensitivity (67%) and specificity (59%), with a positive predictive value of 70%. 5 Your finding of 2-5 WBC/HPF falls well below this threshold.
Major Limitations of Fecal Leukocyte Testing
Fecal leukocyte examination has significant technical and clinical limitations that severely restrict its usefulness:
Morphologic degradation: WBC morphology degrades rapidly during transport and processing, making accurate recognition and quantitation difficult. 1, 6
Intermittent presence: In inflammatory diarrhea, fecal leukocytes are intermittently present and unevenly distributed in stool, significantly limiting sensitivity. 1
Poor specificity: Fecal leukocytes can be present in both infectious and non-infectious conditions, including inflammatory bowel disease, resulting in low specificity. 1
Inpatient vs. outpatient differences: Among inpatients, fecal leukocytes had only 25% sensitivity and did not predict positive stool culture (likelihood ratio 1.9), whereas among outpatients the test performed better (likelihood ratio 5.0). 3
Recommended Alternative Testing
The Infectious Diseases Society of America and American Gastroenterological Association recommend against relying on fecal leukocytes alone to guide antibiotic therapy or distinguish between bacterial, viral, or parasitic causes. 1
Instead, use these superior alternatives:
Stool lactoferrin or calprotectin: These markers are more stable than fecal leukocytes during transport and processing. 1, 6 Lactoferrin latex agglutination can detect ≥200 leukocytes/μL and remains stable even when morphologic leukocytes are destroyed. 6
Definitive microbiologic testing: Obtain stool culture, C. difficile testing, and consider molecular pathogen panels for patients with suspected infectious diarrhea. 2, 1
Clinical context matters: In patients with diarrhea, fever and sudden onset of symptoms may direct differential diagnosis toward infection, requiring bacterial stool culture or PCR and C. difficile toxin testing. 2
Clinical Decision-Making Algorithm
For a patient with 2-5 WBC/HPF on fecal analysis:
Do not use this result alone to initiate empirical antibiotic therapy. 1
Obtain definitive testing: Send stool culture, C. difficile toxin assay, and consider pathogen panels based on clinical presentation. 2, 1
Consider stool lactoferrin or calprotectin if you need to stratify inflammatory vs. non-inflammatory diarrhea, particularly for determining need for endoscopy. 2, 1
Evaluate clinical features: Fever, bloody stool, abdominal pain, and tenesmus have varying predictive values. 2 However, clinical and stool parameters are more useful by their absence than presence in excluding bacterial infection. 7
Inpatient status matters: If this is an inpatient, fecal leukocyte testing has minimal predictive value and routine stool culture may not be indicated unless there are specific risk factors. 3
Common Pitfalls to Avoid
Do not assume bacterial infection: A finding of 2-5 WBC/HPF has poor positive predictive value and could represent inflammatory bowel disease, partially treated infection, or specimen degradation. 1, 7
Do not delay definitive testing: Waiting for fecal leukocyte results before sending cultures wastes time without improving diagnostic accuracy. 1
Consider non-infectious causes: Inflammatory bowel disease patients can have elevated fecal leukocytes during flares, and this finding does not distinguish between infectious and non-infectious inflammation. 2, 1