The liver is one of the most metabolically active organs in the human body, performing essential roles in metabolism, detoxification, protein synthesis, and nutrient storage. Clinical assessment of liver function relies heavily on biochemical tests known as Liver Function Tests (LFTs). These tests evaluate the concentration of enzymes, proteins, and metabolic products in blood, providing insight into hepatocellular integrity, biliary function, and metabolic capacity. Biochemical Basis of Liver Enzymes Liver enzymes serve as critical biomarkers reflecting hepatocyte integrity and metabolic activity. Alanine Aminotransferase (ALT) and Aspartate Aminotransferase (AST) are aminotransferases involved in amino acid metabolism. ALT is primarily localized in hepatocytes, making it a more specific marker of liver injury. AST, although present in the liver, is also found in cardiac and skeletal muscles, which reduces its specificity for hepatic damage. Elevation of these enzymes in serum typically indicates hepatocellular injury, where disruption of the hepatocyte membrane allows intracellular enzymes to leak into the bloodstream. Cholestatic Markers In addition to hepatocellular markers, biochemical analysis also evaluates cholestatic enzymes, mainly: Alkaline Phosphatase (ALP) Gamma-Glutamyl Transferase (GGT) These enzymes are associated with bile canaliculi and biliary epithelium. Elevated levels often indicate obstruction of bile flow or disorders affecting the biliary tract. Bilirubin Metabolism Bilirubin is a degradation product of heme metabolism. In the liver, unconjugated bilirubin is taken up by hepatocytes and conjugated with glucuronic acid through the enzyme UDP-glucuronyl transferase, making it water-soluble for excretion in bile. Disturbances in bilirubin metabolism can result in: Pre-hepatic jaundice (excess hemolysis) Hepatic jaundice (impaired conjugation or hepatocellular damage) Post-hepatic jaundice (biliary obstruction) Thus, bilirubin measurement provides insight into hepatic uptake, conjugation, and excretion processes. Protein Synthesis Markers The liver is responsible for synthesizing most plasma proteins, including albumin and several clotting factors. Reduced albumin levels may indicate chronic liver disease or impaired hepatic synthetic capacity. Additionally, prothrombin time (PT) is frequently evaluated to assess liver function because clotting factors II, VII, IX, and X are synthesized in the liver. Clinical Significance The interpretation of liver function tests requires a biochemical understanding of metabolic pathways and cellular integrity. Patterns of enzyme elevation can differentiate between hepatocellular damage, cholestasis, and synthetic dysfunction. Liver function tests represent a powerful biochemical tool for assessing hepatic health. By analyzing enzyme activity, bilirubin metabolism, and protein synthesis, clinicians can detect early signs of liver dysfunction and guide diagnostic and therapeutic strategies.