My personal experience is that levels as low as 10 mg per day will elevate AST and ALT to borderline high. Doses of 15-20 mg usually push it over.
Here's a study that showed a does-response increase in AST/ALT in a very large randomized double-blind placebo-controlled clinical study with Anavar treated HIV patients at doses of 0, 20, 40, and 80 mg. All doses showed mean elevated AST/ALT levels, increasing with increasing dose within the first 4 to 8 weeks of therapy. Three subjects were discontinued from the 40 mg group and 4 subjects from the 80 mg group due to liver toxicity.
https://www.ncbi.nlm.nih.gov/pubmed/16540931. Full text of the article is available on-line. you have to dig into the paper to find this information.