Detailled Information)

Name of the Instrument/Tool Ankylosing Spondylitis Disease Activity Score (ASDAS)
First Description

Lukas C, Landewé R, Sieper J, Dougados M, Davis J, Braun J, van der Linden S, van der Heijde D; Assessment of SpondyloArthritis international Society. Development of an ASAS-endorsed disease activity score (ASDAS) in patients with ankylosing spondylitis. Ann Rheum Dis. 2009 Jan;68(1):18-24. doi: 10.1136/ard.2008.094870. Epub 2008 Jul 14. PMID: 18625618.

Year 2009
Concept of constructs Disease activity
Population/Disease Disease specific
Originally developed for Axial Spondyloarthritis
Other rheumatic diseases
where can be applied (only if validated)
Additional population with no rheumatic diseases No
Language: Originally published in ---
Available in Language English
Author/s Lukas C,
Title Assessment of SpondyloArthritis international Society. Development of an ASAS-endorsed disease activity score (ASDAS) in patients with ankylosing spondylitis.
Journal Ann Rheum Dis.
Year 2009
Vol 68
Num 1
Pages 18-24.
Country International Study (ASAS group)
Language English
Other references of interest
Brief Description

Ankylosing Spondylitis Disease Activity Score (ASDAS): 2018 update of the nomenclature for disease activity states.

Brief Description

ASDAS, a highly discriminatory ASAS-endorsed disease activity score in patients with ankylosing spondylitis.

Brief Description

Extensive data about sensitivity and discriminatory ability of the ASDAS in patients treated with etanercept or sulphasalazine in the ASCEND trial.

Instrument/Tool Translations References
No other References.
Correspondence to Professor Robert Landewé
E-Mail ---
Address Department of Clinical Immunology and Rheumatology, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1100 DD Amsterdam
Website ---
Available ---

Type Of Measure Composite Index
Brief Description

ASDAS is a composite index with continuous measurement properties. The Assessment of SpondyloArthritis international Society (ASAS) membership has selected the ASDAS containing C-reactive protein (CRP) as acute phase reactant as the preferred version, and the one with erythrocyte sedimentation rate (ESR) as the alternative version. Apart from the value of CRP or ESR, the four additional self-reported items included in this index are back pain (BASDAI question 2), duration of morning stiffness (BASDAI question 6), peripheral pain/swelling (BASDAI question 3) and patient global assessment of disease activity.

Number of Items 5
Range 0 - ≈7 (arithmetically there is no upper limit)
Responses options/scale Yes
peripheral pain/swelling (BASDAI question 3) and patient global assessment of disease activity. Back pain and peripheral pain/swelling are anchored from 0 (none) to 10 (very severe) and patient global assessment is also anchored from 0 (not active) to 10 (very active). Duration of morning stiffness (BASDAI question 6) is anchored by a time scale (0–2 or more hours). The fifth item is the value of one of the acute phase reactants: CRP (in mg/L) or ESR (in mm/h). Items are mathematically combined to give a continuous score - the ASDAS.
Developed for Both
Method of administration Self-administered
Recommendations to score

The formula for ASDAS-CRP (preferred version) is:

0.12 x Back Pain + 0.06 x Duration of Morning Stiffness + 0.11 x Patient
Global + 0.07 x Peripheral Pain/Swelling + 0.58 x Ln(CRP+1)


The formula for ASDAS-ESR (alternative version) is:

0.08 x Back Pain + 0.07 x Duration of Morning Stiffness + 0.11 x Patient
Global + 0.09 x Peripheral Pain/Swelling + 0.29 x √(ESR)


The score is most easily calculated using an online calculator or a hand-held calculator, although it is possible to calculate longhand or using a quick ASDAS calculation form available online. Also, the ASAS group has a mobile application that can be used to calcuulate the score.

Score Interpretation Ranges from 0 (no disease activity) to ≈7 (maximal disease activity), although arithmetically there is no upper limit for ASDAS (upper end of the scale being determined by the level of the CRP or ESR).
Cut-off points 1.3 "inactive" from "low disease activity"; 2.1 "moderate" from "high disease activity"; 3.5 "high" from "very high disease activity"
Cut-off points applied to Both
Smallest detectable change if described 0.41 to 1.06 depending on the method. "clinically important improvement" a change >=1.1 units & "major improvement" a change >=2.0 units
Smallest detectable change applied to Both
Completion time by the patient less than 1 minute minutes
Scoring time by the assessor quick assessment forms (both available at and hand-held calculator but is unwieldy without such a tool. minutes
Training to score Not necessary
Strengths Useful in clinical practice & research, Easy to use
Limitations Complex scoring
Limitations <5 European languages (English)
Observations ---
A. Internal Consistency Tested
Cronbach's (Describe)

Four of the items in the ASDAS are taken from the BASDAI, and these items in general have good reliability.

B. Reliability intraobserver or test-retest Not Tested
Continuous scores: intraclass
correlation coefficient (ICC)
Dichotomus: Cohen kappa (Describe)
C. Reliability interobserver or Measurement error Tested
Standard error of measurement (SEM),
smallest detectable change (SDC) or
Limits of agreement (LoA) (Describe)

Wyrwich SEM = 0.41

SDC = 0.41 to 1.06 depending on the method

A. Content validity: face validity Tested
Expert opinion (relevance and
comprehensiveness) (Describe)

Items were generated by Assessment of Spondyloarthritis international Society (ASAS) members using a 3-round Delphi process.  Only those domains receiving 80% agreement were taken to the next round. Items selected were then tested in an international longitudinal cohort study. There were no patients directly involved in item generation


Generation by an international expert group of rheumatologists (ASAS) interested in AS, and the inclusion of serologic markers of inflammation improves the face validity over solely patient-reported domains.


Extensive statistical analysis has minimized redundancy between items.

B. Construct Validity:
Structural validity
Brief Description

Testing in a three-step statistical approach (principal component analysis, discriminant function analysis and linear regression analsyis) supports structural validity of the ASDAS.

The ASDAS has shown construct validity, as assessed by the correlations between the ASDAS-CRP and patient global assessment (Pearson’s correlation coefficient = 0.74; similar for the ASDAS with ESR [ASDAS-ESR]) as well as the ASDAS-CRP and physician global assessment (Pearson’s correlation coefficient = 0.47).

Hypotheses-testing Tested
Brief Description

Pearson’s correlations between the ASDAS-CRP (ASDAS-ESR) and patient global assessment was 0.72 (0.75), with physician global assessment 0.41 (0.48), with BASDAI 0.75 (0.77) and with BASFI 0.58 (0.56) in the OASIS database.

Cross-cultural validity Not Tested
Brief Description ---
C. Criterion validity Tested
Comparison with a 'gold standard' Continuous scores:
correlations, ROC curves Dichotomus:
Sensitivity & Specificity (Describe)

Excellent discrimination between high and low disease activity states as defined by the physician global assessment (standardized mean difference [SMD] at baseline 1.33 for ASDAS-CRP and SMD 1.55 for ASDAS-ESR) based on the Norwegian disease-modifying anti-rheumatic drug (NORDMARD) database, and between patients treated with TNF blockers and with placebo (SMD 1.50 for ASDAS-CRP and SMD 1.51 for ASDAS-ESR) based on participants in randomized controlled trials of TNF blockers for AS.


AUC ranging from 0.74 to 0.95 against multiple gold-standards based on physician global assessment, patient global assessment and patient global rating of change after treatment.


Cut-off developed were developed using a robust methodology involving ROC curve analyses and have proven to have external validity and a good performance in cross-validation.


In RCTs with TNF-blockers versus placebo, ASDAS improvement scores perform better (higher Qui-squares) than classical improvement criteria (ASAS20, ASAS40, BASDAI50 and change in BASDAI of at least 2 units) and also that ASDAS inactive disease is more discriminative than ASAS partial remission criteria. This has implication is sample size calculation using ASDAS (lower number of patients required for the same power and α level).

Responsiveness Tested
Ability to detect change over
time Multiple methods (Describe)

The ASDAS was sensitive to improvement with TNF inhibitors, with a Guyatt´s ES of 2.4 and 2.2, for ASDAS-CRP and ASDAS-ESR, respectively, compared to an ES of 1.5 for BASDAI.

Interpretability Tested
of responders with the highest/lowest
score Minimal important difference (MID) (Describe)

A change of at least 1.1 units represents “clinically important improvement” and a change of at least 2.0 units represents major improvement.


In treated patients, ASDAS and ASDAS cut-offs show a clear shift from higher towards lower disease activity states.

Other Comments

The ASDAS has been validated in several observational cohorts and trial populations and is now being used regularly in clinical trials, including longitudinal studies of patients with SpA receiving TNFi. The ASDAS has been endorsed by the ASAS and by Outcome Measures in Rheumatology. ASDAS is emerging as the best measure of disease activity in AS/axial SpA on the basis of including both patient-generated items and objective measures of inflammation and on having, to date, equivalent or often superior psychometric performance when compared to the BASDAI. 

Outcome Measure ---
Document 1 ASDAS-CRP_Calculation_Form_updated.pdf
Questionnaire CRP-ASDAS
Document 2 ASDAS CRP
Questionnaire ESR-ASDAS