What does the presence of white blood cells (leukocytes) in stool indicate?

White Blood Cells in Stool: Clinical Significance

Fecal leukocytes should NOT be used to establish the cause of acute infectious diarrhea, as they perform poorly for this purpose and have significant technical limitations. 1

Primary Clinical Interpretation

The presence of white blood cells in stool traditionally suggests inflammatory diarrhea rather than secretory diarrhea, but this distinction has limited clinical utility in modern practice. 1

Key Limitations of Fecal Leukocyte Testing

• Poor diagnostic performance: Fecal leukocyte examination performs poorly to establish the infectious cause of diarrhea, especially among hospitalized patients 1

• Technical degradation: Fecal leukocyte morphology degrades during transport and processing, making accurate recognition and quantitation difficult 1

• Intermittent presence: In inflammatory diarrhea, fecal leukocytes are intermittently present and unevenly distributed in stool, significantly limiting sensitivity 1

• Low specificity: Fecal leukocytes can be present in both infectious and non-infectious conditions, including inflammatory bowel disease 1

When Fecal Leukocytes May Be Present

Infectious Causes

• Invasive bacterial pathogens: Shigella, Salmonella, invasive E. coli, and Campylobacter can cause fecal leukocytes 2

• Shigellosis: Studies show >50 WBC/hpf with any RBCs has only 67% sensitivity and 59% specificity for Shigella infection 2

• Cholera: Surprisingly, fecal leukocytes were detected in 88% of cholera patients, suggesting some inflammatory response even in this classically secretory diarrhea 3

• Pseudomembranous colitis: Intense, diffuse colonic white blood cell activity can be seen with C. difficile infection 4

Non-Infectious Causes

• Inflammatory bowel disease: Both Crohn's disease and ulcerative colitis demonstrate fecal leukocytes 5

• Immune checkpoint inhibitor colitis: Stool inflammatory markers including leukocytes may be present 1

Superior Alternative Testing

Use stool lactoferrin or calprotectin instead of fecal leukocytes when trying to differentiate inflammatory from non-inflammatory diarrhea:

• Lactoferrin: More stable than fecal leukocytes during transport and processing, though also present in inflammatory bowel disease and breast milk 1

• Calprotectin: Established marker of intestinal inflammation, though data for acute infectious diarrhea remain conflicting 1

Clinical Pitfalls to Avoid

• Do not rely on fecal leukocytes alone to guide antibiotic therapy decisions 1

• Do not use fecal leukocytes to distinguish between bacterial, viral, or parasitic causes of diarrhea 1

• Breast-fed infants: Lactoferrin (surrogate for fecal leukocytes) is a normal component of human milk, making interpretation difficult in this population 1

• Timing matters: Specimens must be examined within 2 hours of collection for optimal leukocyte detection 3

Recommended Diagnostic Approach

Instead of fecal leukocyte examination, obtain stool culture, C. difficile testing, and consider molecular pathogen panels for patients with suspected infectious diarrhea. 1

For patients requiring risk stratification, stool calprotectin or lactoferrin can help identify those who may benefit from endoscopy or more aggressive workup, though these should not replace definitive microbiologic testing. 1