Gamma glutamyl transpeptidase (GGT) and lactase dehydrogenase (LDH) are two enzymes found in the liver (and also in many other tissues) and are often included as a part of liver function tests.
The GGT is very sensitive (frequently elevated when no liver disease is apparent) and its use is limited to it conferring liver-specificity to an elevated alkaline phosphatase level. An isolated increase of GGT does not need to be further evaluated unless there are additional clinical risk factors for liver disease e.g. alcohol abuse. The enzyme is increased in a number of liver conditions but usually in conjunction with other enzymes (like AST & ALT). Both AST & ALT are diagnostically more useful than the GGT.
LDH is most often measured to evaluate the existence and severity of acute or chronic tissue damage. As the enzyme is present in many body tissues (especially the heart, liver, kidney, skeletal muscle, brain, blood cells, and lungs), it is insensitive and nonspecific. LDH isoenzymes may be used in differential diagnosis to help determine which organs are likely to be involved. It is commonly measured to monitor damage caused by muscle trauma or injury and to help identify haemolytic anaemia.