AST ALT Ratio for Diagnosis
The ratio of AST to ALT has been used as a diagnostic aid:
AST:ALT ratio of more than 2:1 is characteristic in patients with alcoholic liver disease
a raised AST level out of proportion to the ALT level appears to be caused by a differential reduction in hepatic ALT due to deficiency of the cofactor pyridoxine-5-phosphate.
AST:ALT ratio of more than 2:0 is suggestive of alcoholic liver disease – however this result does not preclude other diagnoses.
A raised ALT level to more than 500 IU/L suggests a diagnosis other than alcoholic liver disease, even if the AST:ALT ratio is greater than 2:0.
Other blood tests also suggestive of the presence of alcoholic liver disease include raised of serum gamma-glutamyltranspeptidase (GGT) level and mean corpuscular volume in viral viral hepatitis.
The AST:ALT ratio, which is typically less than 1:0 (particularly true in patients with hepatitis C), can rise to greater values as fibrosis and cirrhosis develop.
The exact mechanism of AST:ALT ratio alteration in progression of liver disease is unclear, and the correlation with and accuracy in predicting degree of fibrosis and presence of cirrhosis are controversial.
In many forms of acute and chronic liver injury or steatosis (fatty infiltration of the liver), the ratio is less than or equal to 1.
A study of 140 patients with nonalcoholic steatohepatitis (NASH; confirmed by liver biopsy) or alcoholic liver disease found a mean AST/ALT ratio of 0.9 in patients with NASH and 2.6 in patients with alcoholic liver disease (2) within the study population.
87 percent of patients with an AST/ALT ratio of 1.3 or less had NASH (87 percent sensitivity, 84 percent specificity).
The severity of NASH as measured by the degree of fibrosis increased, as did the AST/ALT ratio.
The mean ratio of 1.4 was found in patients with cirrhosis related to NASH.
Wilson’s disease can cause the AST/ALT ratio to exceed 4 (3).
AST:ALT ratios are suggestive of certain conditions.
There is significant overlap between AST:ALT ratios in different conditions, this ratio cannot be relied on exclusively when making a diagnosis