ASDAS Calculator — Ankylosing Spondylitis Disease Activity Score
Calculate the ASDAS-CRP or ASDAS-ESR for axial spondyloarthritis from back pain, morning stiffness, patient global, peripheral joints and CRP or ESR, with the ASAS disease activity state.
How it works
ASDAS-CRP = 0.12 × back pain + 0.06 × morning stiffness duration + 0.11 × patient global + 0.07 × peripheral pain/swelling + 0.58 × ln(CRP mg/L + 1). ASDAS-ESR = 0.08 × back pain + 0.07 × stiffness duration + 0.11 × patient global + 0.09 × peripheral pain/swelling + 0.29 × √ESR. All items 0–10. States: < 1.3 inactive · 1.3 to < 2.1 low · 2.1–3.5 high · > 3.5 very high.
The Ankylosing Spondylitis Disease Activity Score (Lukas et al., Annals of the Rheumatic Diseases 2009) combines three BASDAI questions and a patient global rating with an inflammation marker. ASAS recommends ASDAS-CRP as the preferred version. The disease-activity cut-offs were updated in 2018 (inactive < 1.3, low < 2.1, high 2.1–3.5, very high > 3.5); a fall of 1.1 or more is a clinically important improvement and 2.0 or more a major improvement. If CRP is below 2 mg/L (or undetectable), 2 mg/L is used.
Worked example
Back pain 6, morning stiffness 60 minutes (5 on the scale), patient global 6, peripheral pain 3 and CRP 12 mg/L: ASDAS-CRP = 0.72 + 0.30 + 0.66 + 0.21 + 0.58 × ln(13) = 0.72 + 0.30 + 0.66 + 0.21 + 1.49 = 3.4 — high disease activity (2.1–3.5).
Sources: Lukas C et al. Development of an ASAS-endorsed disease activity score (ASDAS) in patients with ankylosing spondylitis. Ann Rheum Dis 2009 · Machado PM et al. Ankylosing Spondylitis Disease Activity Score (ASDAS): 2018 update of the nomenclature for disease activity states. Ann Rheum Dis 2018
Frequently asked questions
What do ASDAS scores mean?
Below 1.3 is inactive disease, 1.3 to under 2.1 low disease activity, 2.1 to 3.5 high disease activity and above 3.5 very high disease activity (ASAS 2018 update).
Should I use ASDAS-CRP or ASDAS-ESR?
ASDAS-CRP is preferred. Use ASDAS-ESR only when CRP is not available, and do not compare scores from the two versions directly.
What if my CRP is very low?
If CRP is under 2 mg/L or below the lab’s detection limit, use 2 mg/L in the formula — the calculator does this automatically.
What ASDAS change is meaningful?
A fall of 1.1 units or more is a clinically important improvement and 2.0 or more a major improvement; a rise of 0.9 or more marks a flare.
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Clinical decision tool for education and for use by trained clinicians alongside clinical judgement — not a diagnosis and not a substitute for medical assessment. Scores validated in specific populations may not apply to every patient.