I have AS due to the CD. My first symptoms were unbearable hip and lower back pain, so bad I could'nt walk let alone dress myself. Heat pads and an extremely hot shower helped me eventually move and then I woulkd walk as that seemd to ease the pain. (hard to walk when you are in agony though).
My Rheumy did blood tests, xrays and scans that detected the fusing. I dont think bone density tests pick up AS, but I might be wrong.
Good luck and keep us posted.