What is the significance of a high AST level?

Many possibilities. Ast (aspartate aminotransferase) is an enzyme made by liver & muscle which when damaged can leak ast into the bloodstream more than normally. In addition to liver injury (eg from alcohol, overdoses of meds like acetaminophen, viral hepatitis, med side effects, hemochromatosis, fatty liver), ast can be high occur in thyroid disease, adrenal insufficiency, muscle disease. Sometimes no cause is found.