Apply the 2009 ASAS criteria for axial SpA in patients with chronic back pain onset before age 45. Two arms: imaging (sacroiliitis + 1 SpA feature) or clinical (HLA-B27 + 2 SpA features). Covers radiographic AS and non-radiographic axSpA.
📅 ASAS 2009📊 Sens 82.9% / Spec 84.4%📖 Ann Rheum Dis. 2009;68(6):777-783
Classification criteria only. The ASAS criteria are designed for research classification, not clinical diagnosis. Do not use as a standalone diagnostic tool. Always integrate with full clinical assessment, imaging review, and rheumatologic judgment.
Classification Result
Complete the form below
Enter entry criteria and SpA features to determine axial SpA classification.
1
Entry Criteria
Both must be present - if either is absent, ASAS axial SpA criteria do not apply
✓
Chronic back pain ≥3 monthsDuration of back pain is 3 months or longer
✓
Age at back pain onset <45 yearsSymptom onset occurred before the patient's 45th birthday
2
Classification Arms
Patient must satisfy the Imaging Arm OR the Clinical Arm (or both)
🖼
Imaging Arm
Sacroiliitis on imaging + ≥1 SpA feature
Not Met
Sacroiliitis on Imaging (required)
Not present / not assessed
Radiographic sacroiliitisGrade ≥2 bilateral OR grade 3-4 unilateral (modified New York criteria)
MRI sacroiliitisActive inflammation (BME/osteitis) highly suggestive of SpA-associated sacroiliitis
SpA Features - select all present (need ≥1)
0 selected
🧬
Clinical Arm
HLA-B27 positive + ≥2 SpA features
Not Met
HLA-B27 (required for this arm)
Not tested / unknown
HLA-B27 negative
HLA-B27 positive
SpA Features - select all present (need ≥2)
0 selected
Criteria Performance (Rudwaleit et al., 2009 - n=649)
82.9%
Overall Sensitivity
84.4%
Overall Specificity
97.3%
Imaging Arm Specificity
Clinical Notes
What is axial spondyloarthritis? ▼
Axial SpA is a chronic inflammatory arthritis affecting the sacroiliac joints and spine. The ASAS criteria unified two subgroups: radiographic axSpA (ankylosing spondylitis) with definite X-ray sacroiliitis, and non-radiographic axSpA where radiographs are normal but MRI or clinical features are strongly consistent. Both forms respond to TNF inhibitors and IL-17 inhibitors.
What defines radiographic sacroiliitis? ▼
Modified New York criteria grading: Grade 0 = normal; Grade 1 = suspicious; Grade 2 = minimal (sclerosis, blurring); Grade 3 = moderate (erosions, widening/narrowing, partial ankylosis); Grade 4 = complete ankylosis. Radiographic sacroiliitis requires grade ≥2 bilaterally or grade 3-4 unilaterally. Interreader reliability for grade 2 is limited even among experienced readers.
What defines a positive MRI for sacroiliitis? ▼
An ASAS-positive MRI requires active inflammatory lesions - bone marrow edema (osteitis) in the subchondral bone on STIR or contrast-enhanced T1 fat-saturated sequences - that are highly suggestive of SpA. Structural lesions alone (erosions, fat metaplasia, sclerosis, ankylosis) without active inflammation are not sufficient. False positives occur in athletes, postpartum women, and other conditions.
What is inflammatory back pain (IBP)? ▼
ASAS 2009 IBP criteria require age at onset <40 years and at least 4 of 5 features: (1) insidious onset; (2) improvement with exercise; (3) no improvement with rest; (4) nocturnal pain improving upon getting up; (5) alternating buttock pain. Sensitivity 79.6%, specificity 72.4% vs. rheumatologist SpA diagnosis.
Imaging arm vs. clinical arm - when to use each? ▼
The imaging arm (specificity 97.3%) is preferred when sacroiliitis is confirmed on X-ray or MRI and represents about 60% of classified patients. The clinical arm (specificity 83.3%) was designed for when imaging is unavailable, requiring HLA-B27 plus 2 SpA features. Either arm is valid if criteria are met - patients may satisfy both.
How does HLA-B27 factor into the criteria? ▼
HLA-B27 serves two roles. In the clinical arm, it is the mandatory gating requirement. In the imaging arm, HLA-B27 positivity counts as one SpA feature. HLA-B27 is positive in approximately 80-90% of AS patients and 50-70% of nr-axSpA patients, but also in 5-8% of the general population without SpA.
What does "good NSAID response" mean as a SpA feature? ▼
Rapid and striking improvement in back pain within 24-48 hours of a full anti-inflammatory dose of an NSAID (naproxen 500mg BID, diclofenac 75mg BID, indomethacin 50mg TID), with recurrence within 48 hours of stopping. Partial or slow improvement does not qualify.
Can these criteria diagnose axSpA? ▼
No. These are classification criteria validated in patients referred to a rheumatologist with high clinical suspicion. In general populations, false-positive rates increase substantially. Clinical diagnosis requires full rheumatologic assessment integrating symptoms, examination, labs, and imaging.
Primary Source: Rudwaleit M, van der Heijde D, Landewe R, et al. The development of Assessment of SpondyloArthritis international Society classification criteria for axial spondyloarthritis (part II): validation and final selection. Ann Rheum Dis. 2009;68(6):777-783. doi:10.1136/ard.2009.108233
IBP Criteria: Sieper J, van der Heijde D, Landewe R, et al. New criteria for inflammatory back pain in patients with chronic back pain. Ann Rheum Dis. 2009;68(6):784-788.