When do you order stool white blood cells (WBCs) in cases of diarrhea?

When to Order Stool White Blood Cells in Diarrhea

Stool white blood cell examination should not be used to establish the cause of acute infectious diarrhea as it has poor performance characteristics and has been replaced by more specific diagnostic tests. 1

Current Recommendations on Stool WBC Testing

The 2017 Infectious Diseases Society of America (IDSA) guidelines provide clear recommendations against using fecal leukocyte examination:

• Fecal leukocyte examination should not be used to establish the cause of acute infectious diarrhea (strong recommendation, moderate quality evidence) 1
• Stool lactoferrin (a surrogate marker for fecal leukocytes) should also not be used for this purpose 1

Limitations of Stool WBC Testing

Stool WBC testing has several significant limitations:

• Fecal leukocyte morphology degrades during transport and processing, making accurate recognition difficult 1
• Leukocytes are unevenly distributed in stool and intermittently present, limiting sensitivity 1
• Poor performance characteristics, especially among inpatients 1
• Lactoferrin (used as a surrogate marker) is also present in non-infectious inflammatory bowel disease, reducing specificity 1
• In infants consuming human milk, lactoferrin is a normal component, making interpretation difficult 1

Preferred Diagnostic Approaches

Instead of stool WBC testing, the following approaches are recommended:

1. For Suspected Infectious Diarrhea

• Fresh diarrheal stool sample (taking the shape of the container) is the optimal specimen 1, 2
• Culture-independent diagnostic tests (CIDTs) including multiplex molecular assays are preferred 2
• Specific testing based on clinical presentation:
  • For bloody diarrhea: Stool culture with specific testing for Shiga toxin-producing E. coli (STEC) 2
  • For healthcare-associated or post-antibiotic diarrhea: C. difficile testing 1

2. For Specific Clinical Scenarios

Bloody diarrhea:

• Stool culture for Salmonella, Shigella, Campylobacter, E. coli O157:H7 2
• Concurrent Shiga toxin testing to detect both O157 and non-O157 STEC strains 2

Recent antibiotic use or healthcare exposure:

• C. difficile testing in patients >2 years of age 1

Persistent diarrhea (>14 days):

• Consider parasitic infections, especially in travelers 1
• Evaluate for non-infectious causes like inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS) 1

Clinical Value of Other Tests

While stool WBC testing is not recommended, other tests may have clinical value:

• Peripheral white blood cell count and differential may be useful clinically but should not be used to establish etiology of diarrhea 1
• For patients with diagnosed E. coli O157 or other STEC infections, frequent monitoring of hemoglobin, platelet counts, electrolytes, and renal function is recommended to detect early manifestations of Hemolytic Uremic Syndrome (HUS) 1
• Endoscopy or proctoscopic examination should be considered in people with persistent unexplained diarrhea who have AIDS or certain underlying conditions 1

Conclusion

The practice of ordering stool white blood cell tests has been superseded by more accurate diagnostic methods. Modern guidelines strongly recommend against using fecal leukocyte examination or stool lactoferrin detection to establish the cause of infectious diarrhea due to poor performance characteristics and the availability of superior diagnostic alternatives.