From the Guidelines
The diagnostic workup for Ankylosing Spondylitis (AS) should involve a comprehensive approach combining clinical assessment, laboratory tests, and imaging studies, with a focus on MRI of the sacroiliac joints as the most sensitive method for detecting early sacroiliitis, as recommended by the Assessment of SpondyloArthritis international Society (ASAS) criteria 1. The initial evaluation should focus on patients with chronic back pain (lasting more than 3 months) with inflammatory characteristics such as morning stiffness improving with activity.
- Laboratory testing should include HLA-B27 antigen testing, which is positive in 74% to 89% of patients with AS, though it's not diagnostic on its own 1.
- Inflammatory markers including erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) should be measured, as they are often elevated during active disease.
- Complete blood count may show mild anemia of chronic disease. Radiographic imaging is crucial, starting with plain X-rays of the sacroiliac joints and spine to detect sacroiliitis, syndesmophytes, and bamboo spine in advanced cases.
- However, early disease may not show radiographic changes, necessitating MRI which can detect inflammation before structural damage occurs.
- MRI of the sacroiliac joints is particularly sensitive for early sacroiliitis, and should be used as the first imaging method in certain cases, such as young patients and those with short symptom duration 1. The diagnosis is typically based on the ASAS criteria, which include imaging evidence of sacroiliitis plus at least one spondyloarthritis feature, or HLA-B27 positivity plus at least two spondyloarthritis features 1.
- A thorough history should also assess for extra-articular manifestations like uveitis, inflammatory bowel disease, and psoriasis, which can support the diagnosis and guide management. It's worth noting that the ASAS criteria are designed for use in clinical research, not for definitive clinical diagnosis, and that care should be taken to acknowledge this when using these criteria in clinical practice 1.
From the FDA Drug Label
The FDA drug label does not answer the question.