You've posted on the end of an old thread from 2009. But in answer to your question .13 is a little over 1/10, .9 is 9/10, so no, you don't have to assume you are positive.
so abvoiusly if my hep c ab index was .13 i am positive
It sounds like it might be a signal to cutoff test which is done on an antibody test to help determine if the antibodies are false positives or real positives. It would mean for anything at .9 or over, it is a true antibody positive.
What is the name of the test written on your hard copy?
I'm not very familiar with tests but it may be an HCV antibody assay test and you may be borderline.
An antibody test does not confirm the presence of HCV. You would need an HCV RNA PCR test for that.
Hopefully someone who knows will help.