In a patient with chronic bloody diarrhea, would a stool examination for ova and parasites be performed first or a colonoscopy?

From the Guidelines

In chronic bloody diarrhea, I would recommend performing a colonoscopy first rather than checking for stool ova and parasites. This approach is supported by the most recent guidelines for the investigation of chronic diarrhea, which suggest that colonoscopy is the preferred initial investigation for patients over 45 years of age, especially when there is a high risk of neoplasia 1. Colonoscopy allows direct visualization of the colon to identify inflammatory bowel disease (like ulcerative colitis or Crohn's disease), colorectal cancer, or other structural causes of bleeding, which are more common causes of chronic bloody diarrhea in developed countries. During the procedure, biopsies can be taken to confirm diagnoses histologically.

Key Considerations

• Stool studies for ova and parasites are more appropriate when there is a history of travel to endemic areas, immunocompromised status, or when the diarrhea is non-bloody 1.
• Parasitic infections like amebiasis can cause bloody diarrhea but are less common in non-endemic regions.
• The colonoscopy should be performed after appropriate bowel preparation, and patients should be informed about the procedure's risks including perforation, bleeding, and sedation complications.
• If the colonoscopy is negative or inconclusive, then stool studies including tests for ova and parasites, bacterial cultures, and Clostridioides difficile toxin assay would be appropriate next steps in the diagnostic workup.

Diagnostic Approach

• The initial assessment should direct the clinician to determine whether further investigation is necessary and, if so, whether the focus should be on colonic, small bowel, or pancreatic disease 1.
• Most chronic diarrhea is due to colonic disease, and in the absence of clinical evidence for malabsorption, investigations should focus on the lower gastrointestinal tract in the first instance 1.
• Colonic investigations should be age-stratified, in keeping with the risk of neoplasia, which is greater in those with one or more first-degree relatives with colorectal cancer and in males 1.

From the Research

Diagnostic Approach for Chronic Bloody Diarrhea

In cases of chronic bloody diarrhea, the diagnostic approach may involve various tests to identify the underlying cause. The decision to check for stool ova and parasites first or perform a colonoscopy depends on the clinical presentation and suspected etiology.

• The study 2 suggests that specific diagnostic investigation, including stool culture, ova and parasites' search, and endoscopy, can be reserved for patients with severe dehydration, more severe illness, persistent fever, bloody stools, immunosuppression, and for cases of suspected nosocomial infection or outbreak.
• Another study 3 found that investigation of the presence of parasites by stool examination with direct microscopy may be insufficient in patients with gastrointestinal complaints and undergoing endoscopy and colonoscopy. The study recommends the investigation of parasite antigens in the wash/swab materials that can be easily taken during the endoscopy and colonoscopy procedure.
• The use of rapid diagnostic tests (RDTs) and molecular-based stool assays, such as the BD MAX™ Enteric Parasite Panel 4, can provide highly sensitive and specific detection of intestinal protozoan parasites, including Giardia duodenalis, Entamoeba histolytica, and Cryptosporidium spp.

Comparison of Diagnostic Tests

The studies 5, 6, and 4 compared the sensitivity and specificity of different diagnostic tests for detecting parasites in stool samples.

• The Triage Micro Parasite Panel 5 showed high sensitivity and specificity for detecting E. histolytica/E. dispar, G. lamblia, and C. parvum.
• The study 6 compared four RDTs and found that they can be a valuable tool when microscopic expertise is poor and in remote and outbreak settings.
• The BD MAX™ Enteric Parasite Panel 4 provided highly sensitive and specific detection of Giardia duodenalis, Entamoeba histolytica, and Cryptosporidium spp. in human stool samples.

Clinical Considerations

The choice of diagnostic test and approach should be guided by the clinical presentation, patient history, and suspected etiology of the chronic bloody diarrhea.

• The study 2 emphasizes the importance of specific diagnosis and identification of the causative agent in patients with severe symptoms, immunosuppression, or suspected nosocomial infection.
• The study 3 highlights the need for a comprehensive diagnostic approach, including stool examination, endoscopy, and colonoscopy, in patients with gastrointestinal complaints.