Elevated alkaline phosphatase (ALP) is most commonly associated with biliary obstruction because ALP is an enzyme predominantly found in the bile ducts and liver. When there is obstruction in the biliary tree, such as from gallstones or tumors, ALP levels increase due to cholestasis and increased synthesis/release from bile duct epithelial cells. This elevation is a key indicator of cholestatic liver injury and helps differentiate from other causes of liver enzyme abnormalities. In contrast, conditions like renal failure, diabetes mellitus, and hypothyroidism do not typically raise ALP levels significantly.

Reference: Harrison's Principles of Internal Medicine, J. Larry Jameson et al., 20th Edition.