Blood in Stool: What Doctors Rule Out First

Noticing blood in your stool can be alarming. While it’s often caused by minor issues, it can sometimes signal a more serious problem. Doctors use a step-by-step approach to figure out what’s going on and to rule out the most common—or most dangerous—causes first. Here’s how they generally work through the possibilities.

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1. Initial Assessment

Before any tests, your doctor will take a thorough history and perform a physical exam. Key points include:

• Stool characteristics
  • Bright red blood vs. dark or “tarry” stool
  • Blood mixed with stool or coating the surface
• Associated symptoms
  • Pain with bowel movements
  • Changes in bowel habits (constipation, diarrhea)
  • Weight loss, fever, fatigue
• Medication use
  • Blood thinners (e.g., warfarin, aspirin)
  • Nonsteroidal anti-inflammatory drugs (NSAIDs)
• Medical history
  • Known hemorrhoids, inflammatory bowel disease (IBD), liver disease
  • Family history of colon cancer or polyps
• Vital signs and overall stability
  • Blood pressure, heart rate (to assess for significant bleeding)

This initial step helps doctors decide whether you need urgent care (for heavy bleeding or signs of low blood pressure) or can be assessed on an outpatient basis.

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2. Common, Low-Risk Causes

Hemorrhoids

• Swollen veins in the anus or lower rectum
• Cause bright red blood on toilet paper or in the bowl
• Often associated with itching or mild discomfort
• Diagnosed by physical exam or anoscopy

Anal Fissures

• Small tears in the lining of the anus
• Produce sharp pain during bowel movements and bright red blood
• Usually linked to hard stool or constipation
• Diagnosed on exam; often treated conservatively

Both hemorrhoids and fissures are very common and usually benign. They’re often the first causes doctors think of, especially if bleeding is minor and pain is localized.

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3. Diverticular Bleeding

• Diverticula: small pouches that bulge outward through colon wall
• Can bleed suddenly, causing painless, bright red or maroon blood
• One of the most common causes of lower gastrointestinal bleeding (Oakland et al., Gut, 2019)
• Diagnosed by colonoscopy, CT angiography, or tagged red blood cell scan
• Often stops on its own but may require endoscopic or angiographic treatment

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4. Colitis (Inflammatory and Infectious)

Infectious Colitis

• Caused by bacteria (Salmonella, Shigella, Campylobacter), viruses, parasites
• Symptoms: diarrhea (often bloody), abdominal pain, fever
• Diagnosed by stool cultures or PCR tests

Inflammatory Bowel Disease (IBD)

• Ulcerative colitis or Crohn’s disease
• Symptoms: chronic diarrhea, crampy pain, weight loss, fatigue
• Diagnosed by colonoscopy with biopsy

Because colitis can mimic other causes, doctors ask about recent travel, antibiotic use, sick contacts, and check for systemic signs like fever.

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5. Colorectal Polyps and Cancer

• Polyps can bleed intermittently; cancer more likely to cause persistent bleeding
• Risk increases with age (over 50) and family history
• Symptoms may include changes in bowel habits, unexplained weight loss, fatigue
• Screening colonoscopy is the gold standard for detection
• Early removal of polyps prevents progression to cancer

While less common than hemorrhoids or diverticular bleeding, ruling out colorectal cancer is crucial, especially in patients over 45 or with alarm features.

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6. Angiodysplasia

• Abnormal blood vessels in the colon, often in the elderly
• Cause intermittent, painless bleeding
• Diagnosed by colonoscopy, capsule endoscopy, or angiography
• Treatment may include endoscopic coagulation

This tends to be a consideration after ruling out more common causes, particularly in patients with chronic kidney disease or aortic stenosis.

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7. Medication-Induced Bleeding

• NSAIDs can cause ulcers anywhere in the gastrointestinal tract
• Anticoagulants and antiplatelet agents increase bleeding risk
• Doctors review your medication list and may adjust doses or switch drugs
• Sometimes an upper GI source (stomach or duodenum) bleeds and passes through the intestines, appearing as lower GI bleeding

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8. Upper GI Sources and Portal Hypertension

Though “blood in stool” often means lower GI bleeding, dark or “tarry” stool (melena) may come from higher up:

• Peptic ulcers, gastritis, esophageal varices (in cirrhosis)
• Patients with known liver disease undergo evaluation for portal hypertension and variceal bleeding
• Upper endoscopy is used to visualize and treat these sources

References on cirrhosis (Kamath & Wiesner, Hepatology, 2001; D’Amico et al., Journal of Hepatology, 2006) highlight the importance of liver function scores (e.g., MELD) in predicting outcomes if variceal bleeding occurs.

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9. Diagnostic Approach

Doctors decide on tests based on stability and likely source:

1. Stable, mild bleeding
   • Anoscopy or flexible sigmoidoscopy for anorectal causes
   • Colonoscopy for diverticular bleeding, colitis, polyps
2. Moderate to heavy bleeding
   • Emergency colonoscopy after bowel prep
   • CT angiography if colonoscopy is inconclusive
3. Suspected upper GI bleed
   • Nasogastric lavage (sometimes)
   • Urgent upper endoscopy

Lab tests often include:

• Complete blood count (CBC) to assess anemia
• Coagulation profile if on blood thinners
• Liver function tests in patients with known or suspected cirrhosis

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10. When to Seek Urgent Care

Go to the emergency department if you experience:

• Large-volume bleeding (soaking through clothing or bedding)
• Dizziness, lightheadedness, fainting
• Rapid heartbeat or low blood pressure
• Severe abdominal pain or fever

These can be signs of significant bleeding or infection.

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11. What You Can Do

• Note the color, amount, and timing of blood in stool
• Keep track of other symptoms (pain, fever, changes in bowel habits)
• Review your medications and share this list with your doctor
• Consider doing a free, online symptom check for blood in stool to gather your thoughts before your appointment

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12. Final Thoughts

Most causes of blood in stool are benign and treatable. However, some require prompt attention. It’s vital to:

• Be honest with your doctor about all symptoms and risks
• Follow through with recommended tests (anoscopy, colonoscopy, endoscopy)
• Discuss any concerns about cancer risk, especially if you’re over 45 or have a family history
• Seek emergency care for heavy bleeding or signs of shock

Speak to a doctor about anything that could be life threatening or serious. Early evaluation and treatment can make a significant difference in outcomes.