Things in the blood
Ask to see your result. Then look for the C reactive protein and ESR ( sometimes now called PV, Plasma Viscosity ) readings, these indicate whether there is inflammation present.
Ask the doc' to test for HLA B27 - again look up the meaning of this yourself - if you are positive then you may have AS. 98% of AS sufferers have this tissue type, however if you have HLA B27 it does not necessarily mean you have AS.