What is the approach to stool evaluation in patients with diarrhea?

From the Guidelines

Stool evaluation in patients with diarrhea should be guided by the clinical presentation and duration of symptoms, with testing considered for those with severe symptoms, bloody diarrhea, immunocompromised status, or persistent symptoms beyond 7 days, as recommended by the 2017 Infectious Diseases Society of America clinical practice guidelines 1. The approach to stool evaluation involves considering the patient's symptoms, medical history, and potential exposures to determine the most appropriate tests.

• For patients with acute diarrhea (less than 14 days) and no alarm features, laboratory testing is generally not necessary, as most cases are self-limiting viral infections.
• However, stool evaluation should be considered for patients with:
  • Severe symptoms
  • Bloody diarrhea
  • Immunocompromised status
  • Persistent symptoms beyond 7 days The initial evaluation typically includes:
• Fecal leukocytes or fecal lactoferrin to detect inflammatory diarrhea
• Stool cultures to identify bacterial pathogens such as Salmonella, Shigella, Campylobacter, and E. coli O157:H7, as recommended by the guidelines 1
• Testing for Clostridioides difficile toxin in patients with recent antibiotic use or healthcare exposure
• Ova and parasite examination for patients with travel history to endemic areas or prolonged symptoms In cases of persistent diarrhea (>14 days), additional tests may include:
• Fecal calprotectin to screen for inflammatory bowel disease
• Stool for Giardia and Cryptosporidium antigens
• Tests for fat malabsorption such as fecal elastase The timing of specimen collection is important, with samples ideally collected during active symptoms and before antimicrobial therapy is initiated, as noted in the guidelines 1. Multiple specimens (typically three) collected on different days may increase the yield for parasitic infections. This systematic approach to stool evaluation helps identify the underlying cause of diarrhea and guides appropriate treatment strategies, ultimately improving patient outcomes in terms of morbidity, mortality, and quality of life.

From the Research

Approach to Stool Evaluation

The approach to stool evaluation in patients with diarrhea involves several steps and considerations.

• The decision to perform stool testing should be based on the patient's clinical presentation, medical history, and epidemiological factors, as noted in studies 2, 3.
• In acute diarrhea, stool tests are indicated when there is a strong pretest probability of infectious etiology or Clostridioides difficile infection, as suggested by symptoms such as more than three unformed bowel movements per 24 hours, symptoms lasting more than seven days, and circumstances that are suggestive of infection 3.
• Several commercially available rapid tests for bacterial, viral, or protozoal infections may be offered in addition to traditional methods (e.g., culture, microscopy) and provide a result within six hours 3.

Stool Testing Modalities

Various stool testing modalities are available, including:

• Bacterial stool cultures, which can detect pathogens such as Shiga toxin-producing Escherichia coli, Salmonella species, and Campylobacter species 2, 4.
• Ova and parasite tests, which can detect parasites such as Giardia 4, 3.
• Clostridium difficile testing, which can detect the presence of C. difficile toxin 2, 4, 5.
• Molecular tests, such as real-time PCR and next-generation sequencing, which can detect a wide range of pathogens, including viruses, bacteria, and parasites 6.

Reduction of Inappropriate Stool Testing

Efforts have been made to reduce inappropriate stool testing, particularly in cases of nosocomial diarrhea, where the yield of stool cultures and ova and parasite tests is low 4, 5.

• A best practice advisory (BPA) can be implemented to reduce inappropriate stool testing, by firing when a stool culture or ova and parasite order is placed 72 hours after admission for any immunocompetent patient, and offering the option to remove the order 5.
• Education and awareness campaigns can also be implemented to reduce unnecessary stool testing and promote more appropriate use of stool testing modalities 5.