Laboratory Tests for Diarrhea Lasting 2 Weeks

Initial Laboratory Evaluation

For a patient with diarrhea lasting 2 weeks, stool testing should be performed for Salmonella, Shigella, Campylobacter, Yersinia, Clostridium difficile, and Shiga toxin-producing E. coli (STEC), as well as examination for parasites, according to the Infectious Diseases Society of America 1, 2
Complete blood count (CBC), C-reactive protein (CRP), basic metabolic panel (BMP) to assess for inflammation, dehydration, and electrolyte abnormalities, as recommended by the European Society of Gastrointestinal Endoscopy 3
Stool culture for bacterial pathogens (Salmonella, Shigella, Campylobacter, Yersinia) should be performed, as suggested by the Infectious Diseases Society of America 1, 2
Testing for C. difficile toxin, especially if there is history of antibiotic use within the preceding 8-12 weeks, is recommended by the Infectious Diseases Society of America 4, 5
Stool examination for ova and parasites, particularly for Giardia, Cryptosporidium, Cyclospora, and Entamoeba histolytica, should be performed, as recommended by the Infectious Diseases Society of America 1, 3

Stool electrolytes (Na+, K+) should be measured, as recommended by the European Society of Gastrointestinal Endoscopy 6
Consider 75Se-HCAT scan or serum 7α hydroxy-4-cholesten-3-one if bile acid malabsorption is suspected, as suggested by the European Society of Gastrointestinal Endoscopy 6

Stool for occult blood should be tested, as recommended by the Infectious Diseases Society of America 7
Fecal lactoferrin or calprotectin to detect inflammatory processes should be measured, as suggested by the Infectious Diseases Society of America 7
Culture for STEC with specific testing for Shiga toxin should be performed, as recommended by the Infectious Diseases Society of America 1, 4
Monitor hemoglobin and platelet counts if STEC is suspected to detect early signs of hemolytic uremic syndrome, as recommended by the Infectious Diseases Society of America 8

Fecal elastase to assess for pancreatic insufficiency should be measured, as recommended by the European Society of Gastrointestinal Endoscopy 6
Qualitative fecal fat if malabsorption is suspected should be tested, as suggested by the European Society of Gastrointestinal Endoscopy 6

For travelers with diarrhea lasting 14 days or longer, specific testing for intestinal parasites is recommended by the Infectious Diseases Society of America 1, 9
In immunocompromised patients, additional testing should include Cryptosporidium, Cyclospora, Cystoisospora, microsporidia, Mycobacterium avium complex, and cytomegalovirus, as recommended by the Infectious Diseases Society of America 4, 10

Persistent diarrhea with negative initial laboratory workup should be evaluated with endoscopy, as recommended by the European Society of Gastrointestinal Endoscopy 3, 6
Age >45 years (colonoscopy recommended due to increased risk of neoplasia) should be considered for endoscopic evaluation, as suggested by the European Society of Gastrointestinal Endoscopy 6

If initial testing is negative but symptoms persist, consider testing for microscopic colitis, small bowel bacterial overgrowth, inflammatory bowel disease markers, and non-infectious causes, as recommended by the European Society of Gastrointestinal Endoscopy and the Infectious Diseases Society of America 5, 6, 10

Multiple-pathogen nucleic acid amplification tests detect DNA, not necessarily viable organisms, so clinical correlation is essential, as recommended by the Infectious Diseases Society of America 1, 9
Don't forget to test for C. difficile even if the patient has not been hospitalized but has received antibiotics, as recommended by the Infectious Diseases Society of America 4