Detailled Information)

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.

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

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

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

http://www.asas-group.org/research.php?id=01.

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.

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.

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

Wyrwich SEM = 0.41

SDC = 0.41 to 1.06 depending on the method

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.

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).

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.

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).

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.

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.

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.