The ASAS/EULAR 2022 preferred instrument for assessing disease activity in axial spondyloarthritis. Combines four patient-reported questions with serum CRP to produce an objective composite score. Outperforms BASDAI in predicting biologic treatment response and future functional disability.
Original Development
Lukas C, Landewe R, Sieper J, et al.
Ann Rheum Dis, 2009 & Machado et al. Ann Rheum Dis, 2011
1
Back Pain (Neck, Back, Hip)
How would you describe the overall level of AS neck, back, or hip pain you have had? (Past week)
5
0 = No pain 10 = Most severe pain imaginable
0 (None)10 (Most severe)
2
Duration of Morning Stiffness
How long does your morning stiffness last from the time you wake up? (Past week)
5
0 = No morning stiffness 10 = 2 hours or more
0 (None)10 (≥ 2 hours)
3
Peripheral Pain / Swelling
How would you describe the overall level of pain/swelling in joints other than neck, back, and hips? (Past week)
5
Rate any pain or swelling in peripheral joints (e.g. shoulders, knees, ankles, wrists). 0 = None 10 = Most severe.
0 (None)10 (Most severe)
4
Patient Global Assessment
How active was your spondylitis on average during the past week? (Patient global)
5
Patient's overall assessment of disease activity. 0 = Not active 10 = Very active.
0 (Not active)10 (Very active)
5
C-Reactive Protein (CRP)
CRP Value
mg/L
Important: ASDAS-CRP uses CRP in mg/L (same as DAS28-CRP). If CRP is below the detection limit or hsCRP is < 2 mg/L, enter 2 mg/L as the constant value per ASAS guidelines. Normal CRP is typically < 5 mg/L.
📋 What This Calculator Does
The ASDAS-CRP calculates a composite disease activity score for axial spondyloarthritis using a validated weighted formula that combines four patient-reported items (back pain, morning stiffness duration, peripheral pain/swelling, and patient global assessment) with serum CRP. The result categorizes disease activity into four states: inactive, moderate, high, and very high.
ASDAS was developed by the ASAS group to address the limitation of BASDAI, which is entirely patient-reported and therefore less objective. Adding CRP makes ASDAS more responsive to inflammatory disease activity specifically, and better at predicting biologic response and future functional outcomes compared to BASDAI.
📊 Interpreting the Score
ASDAS-CRP
Activity State
Clinical Meaning
< 1.3
Inactive Disease
Treat-to-target goal. ASAS/EULAR recommend aiming for this state.
1.3 to < 2.1
Moderate Activity
Some disease activity. Consider whether current management is optimized.
2.1 to < 3.5
High Activity
Active disease warranting treatment escalation. Standard threshold for biologic initiation.
≥ 3.5
Very High Activity
Severely active disease. Prompt escalation warranted, including consideration of biologic or targeted synthetic DMARD.
Response thresholds: Clinically important improvement (CII) = ASDAS decrease ≥ 1.1. Major improvement (MI) = ASDAS decrease ≥ 2.0. Adapted from Machado et al., 2011.
💡 Pearls and Pitfalls
✓
ASDAS-CRP is now the ASAS/EULAR 2022 preferred tool, not BASDAI. The 2022 ASAS/EULAR treatment recommendations explicitly state that ASDAS-CRP is preferred for assessing disease activity in axial SpA. BASDAI is retained only when ASDAS-CRP cannot be calculated (e.g., when CRP is unavailable). Use ASDAS-CRP as your primary instrument if at all possible.
✓
Use 2 mg/L if CRP is undetectable. The ASDAS formula was validated using conventional CRP. If the CRP result is below the detection limit, or if hsCRP is below 2 mg/L, the ASAS group recommends substituting a constant value of 2 mg/L in the formula. This is explicitly specified in the ASDAS methodology.
✓
Better predictor of biologic response than BASDAI. Multiple cohort studies have shown that high ASDAS (vs. elevated BASDAI) selects patients with higher CRP, lower BASFI, and characteristics associated with better anti-TNF treatment response. ASDAS-selected patients are more likely to benefit from biologic escalation.
⚠
ASDAS does not differentiate axial from peripheral disease activity. ASDAS was designed for axial SpA but includes peripheral joint pain. A patient with predominantly peripheral PsA or reactive arthritis driving the score may not be well-characterized by ASDAS. For PsA, DAPSA is the preferred composite.
⚠
Fibromyalgia significantly confounds ASDAS. Patients with coexisting fibromyalgia will report high patient-reported items (back pain, global) but will typically have low or normal CRP. This pattern produces moderate ASDAS with low CRP contribution, and these patients respond poorly to biologics. Interpret ASDAS in the context of the full clinical picture.
🔬 Evidence
ASDAS was developed by the ASAS (Assessment in SpondyloArthritis International Society) working group, published by Lukas et al. in Annals of the Rheumatic Diseases in 2009. The instrument was derived using data from the ISSAS cohort and cross-validated in the OASIS cohort. Four versions were initially developed; ASDAS-CRP became the standard due to the faster kinetics of CRP compared to ESR and its more direct reflection of current inflammation.
The disease activity state cutoffs (1.3, 2.1, 3.5) and response thresholds (CII ≥ 1.1, MI ≥ 2.0) were established by Machado et al. in Ann Rheum Dis 2011 using a large international dataset. The superiority of ASDAS over BASDAI for predicting outcomes and selecting biologic-responsive patients was demonstrated in multiple registry studies.
View References▾
1
Lukas C, Landewe 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.
2
Machado P, Landewe R, Lie E, et al.Ankylosing Spondylitis Disease Activity Score (ASDAS): defining cut-off values for disease activity states and improvement scores. Ann Rheum Dis. 2011;70(1):47-53.
3
van der Heijde D, Ramiro S, Landewe R, et al.2016 update of the ASAS-EULAR management recommendations for axial spondyloarthritis. Ann Rheum Dis. 2017;76(6):978-991. Notes preference for ASDAS.
4
Molto A, Gossec L, Meghnathi B, et al.An Assessment in SpondyloArthritis International Society (ASAS)-endorsed definition of clinically important worsening in axial spondyloarthritis based on ASDAS. Ann Rheum Dis. 2018;77(1):124-127.
For clinical decision support only. ASDAS-CRP is a monitoring tool for established axial spondyloarthritis. If CRP is below detection, use 2 mg/L per ASAS guidelines. Do not switch between ASDAS-CRP and ASDAS-ESR for longitudinal monitoring. Results require interpretation in the full clinical context by a qualified clinician.