What are the first-line investigations for a patient's stool?

From the Guidelines

For patients presenting with stool-related concerns, first-line investigations should include stool testing for Salmonella, Shigella, Campylobacter, Yersinia, C. difficile, and STEC, especially in those with fever, bloody or mucoid stools, severe abdominal cramping or tenderness, or signs of sepsis. This approach is based on the recommendations from the 2017 Infectious Diseases Society of America clinical practice guidelines for the diagnosis and management of infectious diarrhea 1. The guidelines emphasize the importance of stool testing in specific circumstances, such as in people with symptoms of infectious diarrhea, particularly when accompanied by fever, bloody stools, or severe abdominal pain.

Key considerations for first-line investigations include:

• Stool testing for common bacterial pathogens like Salmonella, Shigella, and Campylobacter, as well as for C. difficile, especially in patients with recent antibiotic use or healthcare exposure 1.
• Testing for STEC, including culture for O157 STEC and detection of Shiga toxin for non-O157 STEC, in patients with bloody stools or severe abdominal pain 1.
• Consideration of testing for other pathogens, such as Yersinia enterocolitica, in patients with persistent abdominal pain or epidemiologic risk factors for yersiniosis 1.
• Evaluation of stool specimens for Vibrio species in patients with large volume rice water stools or exposure to salty or brackish waters, consumption of raw or undercooked shellfish, or travel to cholera-endemic regions 1.

In addition to these specific tests, a comprehensive approach to stool analysis may include:

• Macroscopic examination of stool to note color, consistency, and presence of blood or mucus.
• Microscopy to detect white blood cells, ova, parasites, and fat globules.
• Fecal occult blood testing to detect hidden blood.
• Fecal calprotectin measurement to differentiate between inflammatory and non-inflammatory bowel conditions.

These investigations provide crucial information about infectious causes, inflammatory processes, and potential malignancies, guiding appropriate treatment decisions and determining if further investigations like endoscopy or imaging are necessary. It is essential to interpret the results of these tests in the context of the patient's clinical presentation and epidemiologic risk factors, as recommended by the guidelines 1.

From the Research

First-Line Investigations for Patient's Stool

When investigating a patient's stool, the following tests can be considered as first-line investigations:

• Microscopic examination to check for leukocytes, occult blood, and other abnormalities 2
• Chemical tests to check for fat, sugars, pH, and other substances 2
• Immunologic tests to check for certain proteins and enzymes, such as alpha-1 antitrypsin and calprotectin 2
• Microbiologic tests to check for infectious causes, including bacteria, viruses, and parasites 2, 3, 4
• Macroscopic examination to check the color, consistency, quantity, shape, odor, and mucus of the stool 2

Specific Investigations for Diarrhea

For patients presenting with diarrhea, the following investigations can be considered:

• Stool culture to check for bacterial causes, such as Salmonella, Shigella, and Campylobacter 3, 4
• Stool tests for viral causes, such as rotavirus and norovirus 4
• Tests for inflammatory markers, such as calprotectin, to check for inflammatory bowel disease 2

Specific Investigations for Constipation

For patients presenting with constipation, the following investigations can be considered:

• Digital rectal examination to check for outlet obstruction 5, 6
• Abdominal X-ray to check for fecal impaction 5, 6
• Colonoscopy to check for structural abnormalities 6
• Anorectal manometry to check for functional abnormalities 6