Diarrhea with blood: what diagnoses are most commonly considered?

Diarrhea with blood can be alarming. It often signals inflammation or injury somewhere in your digestive tract. While many causes are mild and resolve on their own, some require prompt medical care. This guide outlines the most common diagnoses to consider and when to seek help.

Common Infectious Causes
Infections are a leading cause of acute bloody diarrhea. Bacteria, parasites or, less commonly, viruses invade or irritate the bowel lining.

• Campylobacter jejuni
– Often follows undercooked poultry or unpasteurized dairy
– Symptoms: crampy pain, fever, sometimes bloody stools
• Salmonella species
– Linked to eggs, poultry, reptiles
– May cause systemic symptoms (fever, headache)
• Shigella species
– Highly contagious; spreads person-to-person
– Frequent, small-volume stools with blood and mucus
• Escherichia coli O157:H7
– Associated with undercooked beef and raw produce
– Can lead to hemolytic uremic syndrome (kidney injury)
• Clostridioides difficile (C. difficile)
– Often follows antibiotic use
– Presents with watery to bloody diarrhea, fever, abdominal pain
• Entamoeba histolytica
– Amoebic dysentery from contaminated water
– Characterized by severe cramps, tenesmus (feeling of incomplete emptying)

Inflammatory Bowel Disease (IBD)
Chronic inflammation of the gut can cause recurrent or persistent bloody diarrhea.

• Ulcerative colitis
– Confined to the colon and rectum
– Continuous areas of inflammation; often starts at the rectum
– Symptoms: urgency, tenesmus, mixed blood and mucus
• Crohn’s disease
– Can affect any part of the GI tract (mouth to anus)
– Patchy inflammation; may cause strictures or fistulas
– May present with abdominal pain, weight loss, extra-intestinal symptoms (e.g., joint pain)

Ischemic Colitis
Reduced blood flow to the colon—often in older adults or those with heart disease—leads to inflammation and bleeding.

• Typical presentation
– Sudden, crampy lower abdominal pain
– Urgent need to defecate, often with bloody diarrhea
• Risk factors
– Atherosclerosis, low blood pressure, dehydration, certain medications (e.g., vasoconstrictors)

Medication- and Radiation-Induced Colitis
Certain drugs or radiation therapy can damage the bowel lining and cause bleeding.

• Nonsteroidal anti-inflammatory drugs (NSAIDs)
– Can cause ulcers anywhere in the GI tract
– May present with occult bleeding or frank blood in stool
• Chemotherapy or pelvic radiation
– Radiation proctitis presents weeks to months after treatment
– Symptoms: diarrhea, urgency, tenesmus, bleeding

Pseudomembranous Colitis
A severe form of C. difficile infection characterized by a “pseudomembrane” on colonoscopy.

• Presents with
– Profuse diarrhea (may be bloody)
– High fever, abdominal tenderness
• Often follows broad-spectrum antibiotics or hospitalization

Less Common but Important Causes
• Colorectal cancer and polyps
– May cause intermittent bleeding; diarrhea less common than obstruction symptoms
– Average-risk screening starts at age 45–50
• Radiation or ischemic proctitis
– Prior pelvic radiation or vascular disease
– Chronic bleeding, diarrhea, urgency
• Vascular malformations (angiodysplasia)
– Usually in older adults; can cause intermittent painless bleeding
• Anal fissures and hemorrhoids
– Can cause bright red blood on toilet paper or surface of stool
– Rarely associated with true diarrhea, but frequent loose stools can irritate the anus

When to Seek Medical Help
Bloody diarrhea can sometimes signal a life-threatening condition. Contact a healthcare provider or go to the emergency department if you have:
• High fever (>101°F or 38.3°C)
• Signs of severe dehydration (dizziness, low urine output, dry mouth)
• Severe or worsening abdominal pain
• Blood clots in stool or large amounts of blood
• Recent antibiotic use or hospitalization (risk for C. difficile)
• Underlying conditions like heart disease or weakened immunity

Self-Assessment and Next Steps
If you’re unsure about the seriousness of your symptoms, consider a free, online symptom check for to help gauge your condition and guide you on next steps.

Diagnosis and Evaluation
Your doctor will take a detailed history (onset, travel, diet, medications) and perform:

• Stool studies for bacteria, parasites, C. difficile toxin
• Blood tests (complete blood count, electrolytes, inflammatory markers)
• Imaging (CT scan) if ischemia or abscess is suspected
• Endoscopy or colonoscopy for direct visualization and biopsies in IBD, ischemia, cancer workup

Treatment Overview
• Infectious colitis: many bacterial infections are self-limited; antibiotics reserved for severe cases or specific pathogens.
• IBD: anti-inflammatory medications, immunosuppressants, biologics.
• Ischemic colitis: supportive care, treat underlying vascular issues; surgery if complications arise.
• C. difficile: discontinue inciting antibiotics, start targeted therapy (vancomycin or fidaxomicin).
• Radiation/medication-induced colitis: discontinue offending agent, use anti-inflammatory treatments or sucralfate enemas.

Key Takeaway
Diarrhea with blood has many potential causes—from common infections to chronic diseases or ischemia. Early evaluation, accurate diagnosis and targeted treatment are essential. Always discuss any serious or persistent symptoms with your healthcare provider. If you experience life-threatening signs (heavy bleeding, severe pain, high fever, dehydration), seek immediate medical attention. Talk to a doctor about your symptoms and management options.