Glucagon is a hormone produced by the pancreas that works opposite to insulin to raise blood sugar levels when they become too low. This test measures glucagon levels in the blood to evaluate pancreatic function and diagnose various metabolic disorders. Glucagon stimulates the liver to release stored glucose and produce new glucose, helping maintain normal blood sugar levels between meals. Elevated glucagon levels can indicate glucagonoma, a rare pancreatic tumor that causes excessive glucagon production, leading to diabetes, weight loss, and a characteristic skin rash. High glucagon levels are also common in poorly controlled diabetes and can contribute to high blood sugar. Low glucagon levels can cause severe hypoglycemia, especially in people with diabetes who may lose their glucagon response. This test is commonly ordered when evaluating unexplained hypoglycemia, suspected pancreatic tumors, or when investigating the causes of difficult-to-control diabetes.