What diagnostic tests are used for ankylosing spondylitis?

Diagnostic tests for ankylosing spondylitis include blood tests, X-ray imaging of the sacroiliac (SI) joints, CT scanning of the SI joints, MRI of the SI joints, and spinal functional assessment. A combination of these modalities helps evaluate the extent of joint damage and aids in differentiating ankylosing spondylitis from other conditions causing similar low back pain. If symptoms such as persistent lumbar or thoracic spinal rigidity impairing turning, or severe nocturnal pain occur, prompt medical consultation and treatment are strongly recommended.

1. Blood Tests:

Venous blood is drawn to assess relevant biomarkers, including inflammatory markers and genetic indicators. Inflammatory markers reflect the degree of systemic inflammation, while genetic testing—particularly for HLA-B27—helps estimate disease susceptibility and supports overall diagnostic evaluation.

2. Sacroiliac Joint X-ray:

X-ray imaging enables visualization of the SI joint space and bony architecture, allowing detection of bone erosion, sclerosis, or narrowing of the joint space. This modality is simple, widely accessible, and ideal for initial screening; it provides a clear view of structural joint changes.

3. Sacroiliac Joint CT Scan:

CT offers higher spatial resolution than conventional X-ray, enabling detection of subtle bony abnormalities that may be missed on X-ray. It clearly delineates minute erosive lesions within the SI joints and helps determine the stage of disease progression, thereby overcoming the limitations of standard radiography in assessing fine structural details.

4. Sacroiliac Joint MRI:

MRI detects early bone marrow edema and soft-tissue inflammation—even before overt structural damage occurs—making it highly sensitive for identifying early-stage disease. It also evaluates the level of intra-articular inflammatory activity, helping determine whether the disease is currently active or quiescent.

5. Spinal Functional Assessment:

This involves standardized physical maneuvers to quantify spinal range of motion, including chest expansion and flexion/extension of the lumbar spine. Measurements document the degree of spinal restriction and track how the disease impacts daily physical function over time, facilitating longitudinal monitoring and comparative follow-up.

In daily life, maintain proper posture while standing and sleeping; perform gentle, regular spinal stretching exercises; avoid prolonged sitting or bending; and preserve spinal mobility to slow the progression of joint stiffness and associated functional limitations.