A 31-year-old man comes to the physician for a 5-month history of stiffness and pain in his lower back. Symptoms are worse in the morning and improve throughout the day. There is no radiation of the pain down the buttocks or legs. He also reports stiffness of his lower back following sitting for prolonged periods of time. On physical examination, the patient is unable to bend forward completely. Which of the following is most likely to confirm the diagnosis?
Antibody titers
DEXA scan
HLA analysis
Measurement of erythrocyte sedimentation rate
X-rays
