Esophageal and gastric variceal bleeding: Esophageal and gastric variceal bleeding is a life-threatening complication of portal hypertension, most commonly caused by liver cirrhosis. These enlarged veins in the esophagus or stomach can rupture suddenly, leading to severe, potentially fatal hemorrhage characterized by vomiting blood (hematemesis), black tarry stools (melena), dizziness, and shock. Without prompt treatment, mortality rates can exceed 40% within the first episode. Diagnosis is typically made through endoscopy, which allows direct visualization and grading of varices based on their size and risk of bleeding.

Hemorrhoidal bleeding: Hemorrhoidal bleeding is a common condition caused by swollen blood vessels in the anal or rectal area, often resulting in bright red blood during or after bowel movements. While typically not life-threatening, persistent bleeding may lead to anemia and significantly impact quality of life. Symptoms include painless rectal bleeding, anal discomfort, or swelling, with severity ranging from mild spotting to more significant blood loss. Diagnosis is usually made through physical examination and anoscopy, though colonoscopy may be recommended to rule out other serious conditions like colorectal cancer, especially in patients over 40 or with alarm symptoms.

Peptic ulcer bleeding: Peptic ulcer bleeding is a serious complication of stomach or duodenal ulcers, characterized by vomiting blood (hematemesis), black tarry stools (melena), or dizziness due to blood loss. This condition affects millions worldwide, often caused by Helicobacter pylori infection, prolonged NSAID use, or excessive acid production. While some ulcers heal without complications, bleeding ulcers require urgent medical attention as severe cases can lead to shock or even death if untreated. Diagnosis is confirmed through endoscopy, which not only identifies the bleeding source but also allows immediate treatment.

Obscure gastrointestinal bleeding (OGIB): Obscure gastrointestinal bleeding (OGIB) refers to persistent or recurrent bleeding from the digestive tract when standard endoscopic examinations (including gastroscopy and colonoscopy) fail to identify the source. This condition accounts for 5%-10% of all gastrointestinal bleeding cases, with lesions predominantly located in the small intestine in about 50% of patients. Symptoms may include fatigue from chronic blood loss, iron deficiency anemia, or intermittent passage of black/tarry stools (melena) and/or maroon-colored blood (hematochezia), depending on the bleeding location and rate. While some cases result from benign conditions like small bowel vascular malformations or ulcers, others may indicate more serious pathologies such as tumors or Crohn's disease.