Fecalysis vs. Recommended Stool Tests for Acute Diarrhea
No, you should not request a basic "fecalysis" (routine stool analysis) instead of the recommended specific stool tests for acute infectious diarrhea, as fecalysis typically includes outdated markers like fecal leukocytes and lactoferrin that should not be used to establish the cause of acute infectious diarrhea. 1
Why Fecalysis is Inadequate
The 2017 IDSA guidelines explicitly recommend against using fecal leukocyte examination and stool lactoferrin detection to establish the cause of acute infectious diarrhea (strong recommendation, moderate evidence). 1 Here's why:
- Fecal leukocytes degrade rapidly during transport and processing, making accurate recognition and quantitation difficult 1
- Intermittent presence and uneven distribution in stool limits sensitivity for detecting inflammatory diarrhea 1
- Lactoferrin lacks specificity as it is present in non-infectious inflammatory bowel disease and in breast milk (making interpretation difficult in infants) 1
- These tests perform poorly at establishing the infectious cause of diarrhea, especially among inpatients 1
What You Should Request Instead
The optimal specimen is a diarrheal stool sample (one that takes the shape of the container) for culture, immunoassay, and molecular testing to detect bacterial, viral, and protozoal organisms. 1
Recommended Testing Approach:
- For bacterial detection: Fresh diarrheal stool is preferred; if unavailable, a rectal swab may be used, though molecular techniques are more sensitive and less dependent on specimen quality 1
- For viral and protozoal agents, and C. difficile toxin: Fresh stool is strongly preferred 1
- Molecular testing (NAAT) is generally more sensitive than traditional culture methods 1, 2
When to Order Stool Testing:
Testing is indicated when there is strong pretest probability suggested by: 2, 3
- >3 unformed bowel movements per 24 hours 2
- Symptoms lasting >7 days 2
- Bloody or mucoid stools 3
- Fever documented in medical setting 1, 3
- Signs of severe dehydration or sepsis 3
- Immunocompromise or recent hospitalization 3
Clinical Context Matters
Most episodes of acute diarrhea in immunocompetent adults are self-limited and do not require diagnostic workup. 4, 3 However, patients with the risk factors above should receive appropriate microbiologic testing rather than basic fecalysis. 1, 2
Common Pitfall to Avoid:
Do not order stool testing on formed stools, as this can result in false positives (particularly for C. difficile colonization) and unnecessary antibiotic therapy. 1 Testing should only be performed on diarrheal stool from symptomatic patients. 1