ASDAS-CRP
Axial Spondyloarthritis Disease Activity Score (CRP version)
- ASAS (Stichting ASAS, NL)
Sources last checked: 2026-10-13
ASDAS-CRP
Axial Spondyloarthritis Disease Activity Score (CRP version)
ASDAS-CRP is the ASAS-preferred version; ASDAS-ESR uses different weights and is not interchangeable. Clinically important improvement is a fall of ≥ 1.1, major improvement ≥ 2.0.
Interpretation
| < 1.3 — inactive disease | |
|---|---|
| 1.3 to < 2.1 — low disease activity | |
| 2.1 to 3.5 — high disease activity | |
| > 3.5 — very high disease activity |
What is the ASDAS-CRP?
The Axial Spondyloarthritis Disease Activity Score (ASDAS) combines back pain, duration of morning stiffness, peripheral pain/swelling, patient global assessment and CRP into a single weighted score. It was developed by the Assessment of SpondyloArthritis international Society (ASAS) and published by Lukas and colleagues in 2009. ASAS prefers the CRP version and has defined four disease-activity states and improvement thresholds.
When to use it
- At follow-up visits in axial spondyloarthritis (radiographic and non-radiographic)
- As the activity measure when starting or escalating biological or targeted synthetic therapy is being discussed
- To assess response: improvement ≥ 1.1 is clinically important, ≥ 2.0 is major
When not to use it
- In rheumatoid arthritis or peripheral-only spondyloarthritis
- Mixing ASDAS-CRP and ASDAS-ESR results in the same patient over time
How it is calculated
ASDAS-CRP = 0.12·back pain + 0.06·duration of morning stiffness + 0.11·patient global + 0.07·peripheral pain/swelling + 0.58·ln(CRP + 1) All patient items on 0–10; CRP in mg/L, with values < 2 mg/L set to 2 mg/L.
Clinical pearls and limitations
- ASDAS-CRP is the ASAS-preferred version; ASDAS-ESR uses different weights and is not interchangeable. Clinically important improvement is a fall of ≥ 1.1, major improvement ≥ 2.0.
- CRP must be in mg/L; values below 2 mg/L (or undetectable) are entered as 2 mg/L, as ASAS specifies.
- The three patient items are taken from BASDAI questions 2, 3 and 6.
- ASAS originally called the 1.3–2.1 range 'moderate'; its calculator now labels it 'low disease activity'.
Frequently asked questions
What ASDAS score is inactive disease?
Below 1.3. 1.3 to < 2.1 is low, 2.1–3.5 high and above 3.5 very high disease activity.
What if CRP is below the detection limit?
Enter 2 mg/L. This calculator applies that rule automatically to any CRP below 2 mg/L.
What is a clinically important improvement in ASDAS?
A fall of at least 1.1 units; a fall of 2.0 or more is a major improvement.
Evidence and guidelines
- Primary source: Lukas C, Landewé R, Sieper J, et al. Development of an ASAS-endorsed disease activity score (ASDAS) in patients with ankylosing spondylitis. Ann Rheum Dis 2009;68(1):18-24.
- ASAS — ASDAS calculator: formulas, CRP < 2 mg/L rule, disease activity states (< 1.3 / < 2.1 / > 3.5) and improvement criteria (Δ ≥ 1.1, Δ ≥ 2.0).
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<p><a href="https://medelix.ai/en/calculators/asdas-crp">ASDAS-CRP calculator by Medelix</a></p>For healthcare professionals and medical students. These tools support, and do not replace, clinical judgement. Always check results against the original source and your local protocols.