Izzy, is the test you mean, HLA-B27? Mine also came out positive (twice). That, along with symptoms, radiographic imaging, history, etc., and I was diagnosed with Ankylosing Spondylitis (AS), too.
Even if the test comes back negative, though, a person can still have AS - just as a test that is positive can mean that a person doesn't have AS or may never develop it.
If you may be interested, Joanna, here is a site about it:
http://www.spondylitis.org/about/as.aspx