Diagnostic Approach to White Pus in Stool

Initial Evaluation

The American Gastroenterological Association recommends immediate stool testing for bacterial pathogens, C. difficile toxin, and parasites, combined with ileocolonoscopy with segmental biopsies to differentiate infectious colitis from inflammatory bowel disease in patients with white pus in stool 1, 2
Routine stool culture for Salmonella, Shigella, Campylobacter, and Shiga toxin-producing E. coli (STEC) is essential for diagnosing bacterial pathogens 2, 3
C. difficile testing is recommended if there is any history of antibiotic use within the preceding 8-12 weeks 2, 4

The European Crohn's and Colitis Organisation recommends ileocolonoscopy with segmental biopsies to establish a definitive diagnosis when pus is present in stool, as no single reference standard exists for diagnosing inflammatory conditions 1, 7
Multiple biopsies from both inflamed and uninflamed segments are essential, as lesions may be focal 1, 7
Segmental biopsies stored in separate containers to map the distribution of inflammation can increase diagnostic accuracy from 66% to 92% 7

The Infectious Diseases Society of America recommends complete blood count with differential, as elevated white blood cell count and neutrophil predominance suggest bacterial infection, while eosinophilia suggests parasitic infection with tissue phase 10
Fecal calprotectin correlates well with endoscopic disease activity in IBD (r > 0.8) and helps distinguish inflammatory from non-inflammatory diarrhea 9

The American College of Gastroenterology recommends testing for Cryptosporidium, Cyclospora, Cystoisospora, and Microsporidia in immunocompromised patients 4, 5
Mycobacterium avium complex and CMV should be tested via endoscopic biopsy in immunocompromised patients 4, 9
Strongyloides serology should be performed in addition to stool testing in immunocompromised patients 9, 5