Retrospective Assessment of Spondyloarthritis Activity With BASDAS Formula

Researchers developed a new equation to calculate the Ankylosing Spondylitis Disease Activity Score based on C-reactive protein (CRP), using only the Bath Ankylosing Spondylitis Disease Activity Index total score and CRP.

The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI)-based Ankylosing Spondylitis Disease Activity Score (BASDAS) is a promising method for classifying patients with axial spondyloarthritis, where disease activity is retrospectively calculated using only the BASDAI total score and C-reactive protein (CRP), according to study results published in Rheumatology.

Study investigators sought to develop and evaluate a new equation used to estimate the ASDAS based on CRP (ASDAS-CRP), using only the BASDAI total score and CRP to retrospectively assess patients with axial spondyloarthritis when individual BASDAI items were unavailable.

Related Articles

The study included 52 patients with axial spondyloarthritis in the derivation cohort who were recruited from the Cordoba Spondyloarthritis Registry and a retrospective sample of 3359 patients in the validation cohort from the Spanish Rheumatology Society National Registry of Spondyloarthropathies and the Ibero American Spondyloarthritis Registry.

Investigators developed the new BASDAS equation to measure disease level with only the BASDAI total score and CRP. Using linear regression analysis, the equation coefficients were determined for the derivation cohort and subsequently validated in the validation cohort. Intraclass correlation coefficients were further calculated to assess the relationship between ASDAS-CRP and BASDAS.

In the derivation cohort, the mean BASDAS value was 2.24±0.90, which was similar to the mean ASDAS-CRP value of 2.23±0.95; these indices were very strongly correlated (r=0.96; P <.001). In the validation cohort, the mean BASDAS value was 2.69±1.13 and the ASDAS-CRP score was 2.62±1.07, which were also very strongly correlated (r=0.96; P <.001). The calculated intraclass correlation coefficients indicated excellent agreement between BASDAS and ASDAS-CRP values in both cohorts, with 0.963 in the derivation cohort and 0.955 in the validation cohort.  

Overall, simplified BASDAS formula performed similarly to the preferred method of ASDAS-CRP to measure disease activity in spondyloarthritis.

Researchers concluded that because the BASDAS can be calculated using only the BASDAI total score and CRP, old data from retrospective studies may now be evaluated according to the currently proposed standard, which is especially promising when individual items of the BASDAI are unavailable.


Aranda-Valera IC, Garrido-Castro JL, Ladehesa-Pineda L, et al. How to calculate the ASDAS based on C-reactive protein without individual questions from the BASDAI: the BASDAI-based ASDAS formula [published online October 19, 2019]. Rheumatology. doi:10.1093/rheumatology/kez480