From the Guidelines
For patients presenting with diarrhea, stool testing should be performed for Salmonella, Shigella, Campylobacter, Yersinia, C. difficile, and STEC in people with diarrhea accompanied by fever, bloody or mucoid stools, severe abdominal cramping or tenderness, or signs of sepsis 1. When evaluating diarrhea, several tests may be ordered depending on severity and duration. Initial testing typically includes a stool analysis to check for blood, white blood cells, and fat content.
Key Tests
- Stool culture can identify bacterial pathogens like Salmonella, Shigella, Campylobacter, and E. coli.
- Specific tests for Clostridioides difficile are important, especially after antibiotic use or hospitalization.
- Parasite testing includes ova and parasite examination and specific tests for Giardia and Cryptosporidium.
- Blood tests may include complete blood count to assess for infection or anemia, electrolytes to check for imbalances, and kidney function tests.
Additional Considerations
In persistent cases, additional tests might include:
- Celiac disease antibodies
- Thyroid function tests
- Inflammatory markers For chronic diarrhea lasting over four weeks, endoscopy or colonoscopy may be recommended to visualize the digestive tract and obtain tissue samples 1. These tests help determine whether the diarrhea is caused by infection, inflammation, malabsorption, or other conditions, guiding appropriate treatment strategies.
Special Populations
In immunocompromised people with diarrhea, a broad differential diagnosis is recommended, including evaluation of stool specimens by culture, viral studies, and examination for parasites 1. People with acquired immune deficiency syndrome (AIDS) with persistent diarrhea should undergo additional testing for other organisms, including Cryptosporidium, Cyclospora, Cystoisospora, microsporidia, Mycobacterium avium complex, and cytomegalovirus 1.
From the Research
Diagnostic Tests for Diarrhea
- Stool evaluation and the predominant stool characteristic, i.e., bloody, watery, and fatty diarrhea, may narrow the differential diagnosis 2
- Microbiological tests and colonoscopic biopsy analysis can identify infectious agents, including bacteria, viruses, and protozoa, in chronic bloody/inflammatory diarrhea 2
- Fecal osmotic gap may help to characterize whether a chronic diarrhea is osmotic or secretory 2
- Stool multiplex polymerase chain reaction (PCR) testing has high sensitivity, short turnaround time, and ability to detect multiple organisms simultaneously 3, 4
- Stool multiplex PCR test detected considerably more bacterial pathogens than stool culture 3, 4
Laboratory Investigations
- Stool culture can detect bacterial pathogens, but has lower detection rate compared to stool multiplex PCR 3, 4
- Fecal calprotectin is a marker for intestinal mucosal inflammation and can be used to evaluate the efficacy of stool multiplex PCR in acute infectious diarrhea 4
- C-reactive protein and sigmoidoscopy-detected colitis are independent factors in stool PCR-based detection of bacterial pathogens 4
Clinical Evaluation
- History taking is a crucial step in diagnosing diarrhea, including onset and frequency of symptoms, stool character, and evaluation of exposures and risk factors 5, 6
- Physical examination should include evaluation for signs of dehydration, sepsis, or potential surgical processes 5
- A comprehensive patient history can be taken using a step-by-step process, including active listening, empathetic communication, and cultural sensitivity 6