دکتر محمد قهری
The AST:ALT ratio (De Ritis ratio) may assist in differentiating the site of biliary obstruction. When associated with a cholestatic picture, a AST:ALT ratio of <1.5 suggests an extrahepatic obstruction.
An AST:ALT ratio of >1.5 indicates intrahepatic (mechanical or medical) cholestasis is more likely.
Drug-induced cholestasisusually presents with a preferential rise in ALP, rather than GGT, or with an ALT:ALP ratio of <2.
Causative drugs would include: antibiotics, immunosuppressants, tricyclic antidepressants and angiotensin converting enzyme inhibitors.
In Primary Biliary Cirrhosis, an autoimmune condition of the intrahepatic biliary ducts, the level of ALP is generally greater than that of GGT. In this case, transaminases are invariably normal or only minimally elevated. Both the European Association for study of the liver and the American Association for study of liver disease recommend that a diagnosis of PBC may be based on cholestatic liver enzyme levels in conjunction with the demonstration of antimitochondrial antibodies. If either of two criteria is absent, imaging and liver biopsy become necessary.
As with PBC, liver enzymes play a key role in the diagnosis of Primary Sclerosing Cholangitis (PSC).
When other causes of liver disease have been excluded, a raised GGT, and particularly ALP, are diagnostic when associated with typical Endoscopic Retrograde Cholangiopancreatography(ERCP) or Magnetic Resonance Cholangiopancreatography(MRCP) findings. This can preclude the need for a liver biopsy. Transaminases levels may be raised up to 2-3 times normal values in PSC but this is not diagnostic. AST is a component of the Mayo Risk Score, which calculates the risk of disease progression in PSC. A high Mayo Risk Score , and an AST:ALT ratio of>1.12 have been shown to be indicators of risk for the development of oesophageal varices. In PSC, as with other liver diseases, there are suggestions that an AST:ALT ratio of >1 indicates the development of cirrhosis.
Alcohol induces hepatic enzymes leading to a raised GGT with an ALP which may be normal, or disproportionately lower than the GGT. A GGT:ALP ratio >2.5 in association with jaundice suggests alcohol as a cause of liver disease. The presence of a macrocytosis, due to either an associated dietary deficiency of folate or B12, or due to a direct suppression of bone marrow by alcohol is supportive of the diagnosis of alcoholic liver disease. A raised GGT is not diagnostic of alcoholic abuse, with research showing it remains high in former drinkers as well as current drinkers. In men, the highest levels of GGT occur in those who drink daily. In women, binge drinkers and those consuming alcohol without food will have especially high levels.
Rf.
Hall P, Cash J. What is the Real Function of LiverFunction Tests? Ulster Med J 2012;81(1): 30-36
