Gastroesophageal Reflux Disease (GERD): This condition is a common cause of upper abdominal pain, including the left upper quadrant, due to stomach acid reflux into the esophagus, causing discomfort and pain.
Peptic Ulcer Disease: Ulcers in the stomach or duodenum can cause left upper quadrant abdominal pain, especially if the ulcer is located on the greater curvature of the stomach.

Gastritis: Inflammation of the stomach lining can cause left upper quadrant pain, often accompanied by nausea, vomiting, and loss of appetite.
Pancreatitis: Although pancreatitis typically causes mid-abdominal pain, it can radiate to the left upper quadrant, especially if the tail of the pancreas is involved.
Splenic Infarction or Rupture: Conditions affecting the spleen, such as infarction or rupture, can cause severe left upper quadrant pain, often accompanied by systemic symptoms like fever and chills.
Diverticulitis: Inflammation of a diverticulum in the colon, particularly in the sigmoid colon, can cause left upper quadrant or left lower quadrant pain.

Myocardial Infarction: Cardiac conditions like myocardial infarction can cause referred pain to the left upper quadrant, making it crucial to consider cardiac causes in patients with risk factors.
Pulmonary Embolism: Although less common, pulmonary embolism can cause referred pain to the abdomen, including the left upper quadrant, especially if the embolism involves the lower lobes of the lungs.
Aortic Dissection: A tear in the aorta can cause severe, tearing pain that may radiate to the left upper quadrant, among other areas, and is a medical emergency.
Ectopic Pregnancy: In women of childbearing age, ectopic pregnancy is a critical diagnosis not to miss, as it can cause abdominal pain, including in the left upper quadrant, along with other symptoms like vaginal bleeding.

Splenic Artery Aneurysm: A rare condition where an aneurysm forms in the splenic artery, which can cause left upper quadrant pain if it ruptures.
Left Upper Quadrant Hernias: Although rare, hernias in the left upper quadrant, such as a diaphragmatic hernia, can cause pain and discomfort in this area.
Gastric Cancer: While not the first consideration, gastric cancer can cause left upper quadrant pain, especially in older adults or those with risk factors like a family history of gastric cancer.
Pancreatic Cancer: Tumors in the pancreas, particularly in the tail, can cause left upper quadrant pain, weight loss, and other systemic symptoms.