Bloody diarrhea: what conditions cause it, and what tests usually come next?

Bloody Diarrhea: Causes and Next Steps

Bloody diarrhea—defined as loose or watery stools mixed with visible blood—can range from a mild, self-limited issue to a sign of serious illness. While it’s natural to feel concerned, understanding common causes and typical tests can help you know what to expect and when to seek prompt care.

Common Causes

1. Infectious Diarrhea
   • Bacterial

   • Salmonella, Shigella, Campylobacter, Escherichia coli O157:H7
   • Often linked to undercooked meat, unpasteurized dairy, contaminated water
     • Clostridioides difficile
   • Follows antibiotic use or hospitalization
   • Can cause severe colitis and pseudomembranes
     • Parasitic
   • Entamoeba histolytica (amebiasis)
   • More common in travelers or areas with poor sanitation

2. Inflammatory Bowel Disease (IBD)
   • Ulcerative Colitis

   • Continuous inflammation of the colon lining
   • Symptoms: bloody diarrhea, urgency, tenesmus (feeling of incomplete emptying)
     • Crohn’s Disease
   • Can affect any part of the GI tract
   • May cause segmental ulceration leading to bleeding

3. Ischemic Colitis
   • Reduced blood flow to part of the colon
   • Presents with sudden crampy pain, urgency, and bloody stools
   • More common in older adults or those with vascular disease

4. Radiation or Medication-Related Colitis
   • Pelvic radiation for cancer can injure colon lining
   • Nonsteroidal anti-inflammatory drugs (NSAIDs) may cause ulcers

5. Colonic Neoplasia
   • Colon polyps or cancer can ulcerate and bleed
   • Usually in older adults or those with family history

Less Common Causes

• Hemorrhoids or Anal Fissures
  • Bright red blood on stool surface
  • Often painful (fissures) or associated with straining (hemorrhoids)
• Portal Hypertensive Colopathy
  • In patients with advanced liver cirrhosis (Tsochatzis et al., 2014)
  • Fragile mucosal vessels can bleed, sometimes mixed with diarrhea
• Infective Colitis from Unusual Organisms
  • Yersinia, Vibrio species
  • Often linked to specific exposures (e.g., oysters for Vibrio)

Initial Evaluation

A thorough history and physical exam guide further testing. Key points include:

• Onset and duration of symptoms
• Travel history, food exposures, antibiotic use
• Associated symptoms: fever, abdominal pain, weight loss
• Past medical history: IBD, cirrhosis, recent hospitalizations
• Medication review (NSAIDs, antibiotics, immunosuppressants)

Physical Exam

• Vital signs: fever, tachycardia (could signal dehydration or sepsis)
• Abdominal exam: tenderness, guarding, distension
• Anorectal exam: fissures, hemorrhoids, masses

Laboratory and Stool Studies

1. Stool Cultures and Pathogen Panels

   • Culture for Salmonella, Shigella, Campylobacter
   • Shiga-toxin assay for E. coli O157:H7
   • Clostridioides difficile toxin or PCR
   • Parasite ova and antigen tests (e.g., Entamoeba)

2. Fecal Leukocytes or Lactoferrin

   • Indicates inflammation in the colon
   • High levels often correlate with invasive bacterial infection or IBD

3. Blood Tests

   • Complete Blood Count (CBC):
     • Hemoglobin/hematocrit (degree of blood loss)
     • White blood cells (infection, inflammation)
   • Comprehensive Metabolic Panel (CMP):
     • Electrolytes (dehydration)
     • Kidney and liver function
   • Inflammatory Markers:
     • C-reactive protein (CRP), erythrocyte sedimentation rate (ESR)
   • Coagulation Studies (if cirrhosis is suspected)

Imaging and Endoscopy

1. Abdominal CT Scan

   • Identifies colonic wall thickening, abscesses, vascular problems
   • Helpful when physical exam suggests severe disease or complications

2. Colonoscopy with Biopsy

   • Gold standard for diagnosing IBD, ischemic colitis, malignancy
   • Direct visualization and tissue sampling

3. Flexible Sigmoidoscopy

   • Useful for rapid assessment of the distal colon
   • Often sufficient if disease appears limited to rectum/sigmoid

4. Transient Elastography or Fibrosis Scores

   • If portal-hypertensive colopathy is a concern (cirrhosis)
   • Noninvasive liver stiffness testing (e.g., FibroTest, APRI) (Castera et al., 2005)

Special Considerations

• Travelers and Immunocompromised:
  Consider unusual pathogens (e.g., Cyclospora, Mycobacterium avium).
• Severe Presentations:
  High fever, hypotension, abdominal distension or peritonitis signs require urgent imaging and surgical consult.
• Chronic Bloody Diarrhea:
  Suspect IBD or neoplasia; endoscopic evaluation is key.

Next Steps and When to Seek Help

If you notice persistent or worsening symptoms, or any of the following “red flags,” seek medical attention promptly:

• High fever (>102°F/39°C)
• Severe abdominal pain or distension
• Dizziness or fainting (signs of low blood pressure)
• Inability to tolerate oral fluids
• Signs of anemia (pallor, rapid heartbeat)

You might also consider doing a free, online symptom check for bloody diarrhea to help clarify your concerns and decide when to see a healthcare provider.

Speak to a Doctor

While many cases of bloody diarrhea resolve with supportive care and targeted treatment, some can be life-threatening. If you experience any serious symptoms or if you have risk factors such as advanced age, cirrhosis, immune suppression, or an underlying bowel disease, talk to a doctor right away. Early diagnosis and appropriate testing—stool studies, blood work, imaging, or endoscopy—can make a critical difference in outcomes.