Final answer:
Alkaline phosphatase is an enzyme that becomes sensitive and elevated with biliary obstruction, signaling potential liver issues before bilirubin rises. Its elevation is not exclusive to liver conditions and can indicate bone growth or disease.
Step-by-step explanation:
Alkaline phosphatase is much more sensitive to biliary obstruction and is usually elevated before bilirubin levels rise. This enzyme is present in the cells lining the biliary ducts of the liver, and plays a role in bone remodeling and placental tissue, indicating it isn't specific only to liver function. Increased alkaline phosphatase levels can be seen in a variety of conditions, including acute liver damage, intrahepatic cholestasis, or infiltrative diseases of the liver. It's also elevated in growing children and elderly patients with Paget's disease. The ratio of AST to ALT can help differentiate between various causes of liver damage. While ALP levels are a marker of cholestasis and liver function, they can also indicate normal bone growth or disease.