🩸 Understanding Upper vs Lower GI Bleeding: Pathophysiology & Clinical Clues

Gastrointestinal (GI) bleeding is a common and potentially serious problem in medicine. Some cases involve chronic, slow blood loss, leading to anaemia, while others can result in massive haemorrhage, requiring urgent intervention.

To effectively manage GI bleeding, doctors need to identify the source, which falls into two broad categories:

• Upper GI Bleeding (UGIB): 

• The bleeding comes from areas above the ligament of Treitz, meaning it starts in the oesophagus, stomach, or first part of the small intestine (duodenum).

• Lower GI Bleeding (LGIB): 

• The bleeding originates from below the ligament of Treitz, meaning it occurs in the jejunum, ileum, colon, or rectum.

Recognising whether the bleeding is from the upper or lower part of the digestive tract is critical for choosing the right treatment.

🔬 Pathophysiology: What’s Causing the Bleeding?

🔴 Upper GI Bleeding

Most upper GI bleeding occurs due to damage to the lining of the oesophagus, stomach, or duodenum, or because of fragile blood vessels under high pressure.

Common Causes

1️⃣ Peptic Ulcer Disease

How it happens: Normally, the stomach and duodenum have a protective lining to resist strong stomach acid. However, certain factors—such as infection by Helicobacter pylori bacteria or long-term use of painkillers like ibuprofen or aspirin—can weaken this lining.

Why ulcers bleed: When the protective lining is damaged, acid starts eroding the tissue deeper, eventually exposing small arteries. This results in persistent bleeding into the stomach or duodenum.

Key clue: Patients may vomit dark brown or black blood (called "coffee-ground" vomitus).

2️⃣ Oesophageal Varices

How it happens: In people with severe liver disease (such as cirrhosis), blood flow through the liver becomes blocked, increasing pressure in the veins of the oesophagus. These veins stretch and enlarge, becoming fragile and prone to rupturing.

Why varices bleed heavily: Unlike normal blood vessels, these thin-walled veins lack the ability to constrict, meaning once they burst, blood flow continues unchecked.

Key clue: A patient with chronic liver disease may suddenly vomit large amounts of bright red blood, a medical emergency requiring urgent intervention.

3️⃣ Mallory-Weiss Tears

How it happens: Forceful vomiting causes small tears in the lower oesophagus near where it connects to the stomach.

Why these bleeds are usually mild: The tear is superficial, affecting only the surface layers of the tissue, which means bleeding often stops on its own.

Key clue: A patient reports severe nausea and vomiting, followed by small amounts of red-streaked blood in their vomit.

🔵 Lower GI Bleeding

Bleeding in the lower digestive tract is usually caused by fragile blood vessels, inflammation, or structural abnormalities.

Common Causes

1️⃣ Diverticular Disease

How it happens: In older adults, small pouches (diverticula) develop in the colon wall. These pouches form where blood vessels pass through the muscle layers, making those spots structurally weak.

Why diverticular bleeds can be brisk: If one of these blood vessels ruptures, the bleeding is fast and sudden, but not painful because there is no inflammation.

Key clue: A patient passes large amounts of bright red blood without abdominal pain or discomfort.

2️⃣ Angiodysplasia

How it happens: Over time, small blood vessels in the intestine can become misshapen and fragile. This condition is common in older adults and leads to slow, intermittent bleeding.

Why bleeding is hard to detect: The blood loss is usually small but frequent, meaning it doesn’t cause dramatic symptoms until anaemia develops.

Key clue: A (usually elderly) patient has chronic tiredness and low iron levels, but no obvious bleeding events.

3️⃣ Inflammatory Bowel Disease (IBD)

How it happens: In conditions like ulcerative colitis and Crohn’s disease, chronic inflammation damages the lining of the intestines, causing ulcers that bleed.

Why bleeding is different from diverticular disease: Unlike diverticular bleeds, IBD-related bleeding is accompanied by abdominal pain and diarrhoea.

Key clue: A young patient reports recurrent episodes of bloody diarrhoea, abdominal cramping, and fatigue.

🩺 Clinical Reasoning: Identifying the Source

When a patient presents with GI bleeding, your job is to determine whether it is upper or lower, estimate how severe the blood loss is, and guide the next steps in treatment.

🔍 Upper GI Bleeding Clues

✅ Vomiting blood: Bright red (fresh) or "coffee-ground" (digested blood).

✅ Black, tarry stools (melaena): Due to digested blood passing through the intestines.

✅ Epigastric (upper abdominal) pain: Suggests a stomach or duodenal ulcer.

✅ Signs of chronic liver disease: Think varices if the patient has jaundice, ascites, or a history of high alcohol use.

✅ Elevated urea: Blood digestion increases urea:creatinine ratio.

Melaena

🔍 Lower GI Bleeding Clues

✅ Bright red rectal bleeding: Indicates fresh blood from the lower colon or rectum (haematochezia)

✅ Painless, large-volume bleeding: Often diverticular disease or angiodysplasia.

✅ Bloody diarrhoea + abdominal pain: Suggests inflammation, like ulcerative colitis.

✅ Chronic anaemia: Think colorectal cancer or slow angiodysplastic bleeding.

✅ Normal or low urea levels: No digested blood in the stomach.

⚠️ Clinical Pitfalls

❌ Massive upper GI bleeds can mimic lower GI bleeding—if transit is fast, blood may appear bright red rather than black.

❌ Silent bleeds from NSAID ulcers may lead to anaemia, not dramatic haemorrhage.

❌ Small bowel bleeding (from tumours or vascular malformations) requires capsule endoscopy if conventional scopes miss the source.

🩺 Case Studies

Case 1: A Silent Peptic Ulcer

Patient: A 52-year-old man reports fatigue and shortness of breath, but no obvious bleeding.

History: He takes ibuprofen daily for arthritis.

Why this is concerning:

✅ His symptoms suggest chronic blood loss, likely from a small but persistent stomach ulcer.

✅ The ulcer isn’t causing pain, but is slowly oozing blood, leading to iron-deficiency anaemia.

✅ Without treatment, this could progress to severe bleeding or perforation.

Case 2: Variceal Bleeding & Shock

Patient: A 58-year-old man with liver cirrhosis suddenly vomits large amounts of bright red blood.

History: Long-term alcohol use, previously diagnosed with liver disease.

Why this is a medical emergency:

✅ Oesophageal varices have ruptured, causing severe blood loss in minutes.

✅ He may quickly go into shock—low blood pressure, rapid heartbeat, cold clammy skin.

✅ Immediate resuscitation is needed: IV fluids, medications to reduce pressure in varices, and urgent endoscopy to stop bleeding.

Case 3: Sudden, Painless Rectal Bleeding

Patient: A 74-year-old woman wakes up to find bright red blood in the toilet but feels fine.

History: She has a history of diverticulosis, occasional constipation.

Why diverticular bleeding can be misleading:

✅ No pain—patients may assume bleeding isn’t serious, but it can be high-volume.

✅ Blood loss may be brisk, requiring monitoring of haemoglobin levels.

✅ Bleeding often stops on its own, but large bleeds may require a scan or colonoscopy to confirm the source.

📌 Key Takeaways

• Upper GI bleeding = vomiting blood or black stools; common causes include ulcers and varices.
• Lower GI bleeding = bright red rectal bleeding; often due to diverticular disease or inflammation.
• Always check the patient's haemodynamic status and stabilise the patient first before ordering tests.

Want to keep learning?

• 📝 Complete the quiz on this topic →
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