Laboratory investigations include :

  • Blood test
    • ESR (erythrocyte sedimentation rate) is usually raised due to infection.
    • C-reactive protein is usually raised due to inflammation


  • Serology test
    • For rheumatoid factor & anti nuclear antibody : Both the tests are negative in Ankylosing spondylitis.
    • HLA-B27 gene : This is positive in 90% of cases of Ankylosing spondylitis.


  • X-Ray shows
    • Signs of sacroilitis (inflammation of hip joint) in lower part of joints with irregularity and marginal sclerosis, finally progressing to fusion.
    • Squaring of vertebras in lumbar spine ( due to fusion of anterior and lateral ligaments, syndesmophytes formation, erosion and sclerosis of anterior corners of vertebra)giving an appearance of ‘bamboo spine’ or ‘rail road track’.
    • Signs of osteoporosis may be seen in later stages.


  • ECG, Lung function test and Renal function test : In case of involvement of heart, lung or kidney respectively.