The liver is the largest gland in the body. Lobuli represent a functional liver unit and are composed of liver cells called hepatocytes. If hepatocytes are damaged, the liver enzymes are released resulting in a rise of enzyme concentration in the blood stream. Laboratory liver tests are useful in the evaluation of hepatic dysfunction. The basic routine test mainly determines activity of aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, lactate dehydrogenase, gamma-glutamyl transferase and aldolase. Aminotransferases participate in the metabolism of amino acids and carbohydrates. Gamma-glutamyl transferase is found at the cell membrane in different tissues where it plays an important role in the regeneration of cellular oxidant, glutathione. Alkaline phosphatase is a metalloenzyme that catalyzes the removal of phosphate groups from nucleotides, proteins and other molecules. Activity of alkaine phosphatase affect the membrane transport of phosphate through specific carriers so that phosphate is delivered in certain cellular parts, eg. for synthesis of nucleotides. Lactatedehydrogenase catalyzes the reversible conversion of pyruvate into lactate with NADH as a cofactor. Its activity is the highest in cells that do not contain mitochondria. Aldolase exist in two isoforms. In liver cells, aldolase B is the active form. Due to its high affinity for fructose 1-phosphate, aldolase B is the key enzyme in the fructose metabolism.