Which lab marker may be helpful in diagnosing ankylosing spondylitis?

HLA-B27 is a specific antigen that is strongly associated with ankylosing spondylitis (AS), a type of inflammatory arthritis that primarily affects the spine and can lead to severe, chronic pain and rigid deformity. The presence of HLA-B27 is considered a significant risk factor for developing AS. While not all individuals who are HLA-B27 positive will develop the disease, the majority of patients with ankylosing spondylitis are found to carry this antigen. Its detection can thus support the diagnosis when evaluating a patient with symptoms suggestive of this condition.

In contrast, RF factor and anti-CCP antibodies are more commonly associated with rheumatoid arthritis, making them less relevant for diagnosing ankylosing spondylitis. C-reactive protein, while it can indicate systemic inflammation and may be elevated in patients with AS, is not specific to this condition and can be present in various inflammatory states. Thus, HLA-B27 serves as a more direct marker for ankylosing spondylitis diagnosis compared to the other options.