Defining functioning categories in axial Spondyloarthritis: the role of the ASAS Health Index

The Assessment of SpondyloArthritis international Society Health Index (ASAS HI) is an inclusive questionnaire, able to describe the total impairments and restrictions due to axial spondyloarthritis (axSpA). Considering the relationship between ASAS HI and the Ankylosing Spondylitis Disease Activity Score (ASDAS)-CRP, the aim of this study is to establish the ASAS HI cut-off values for functioning categories employing the ASDAS-CRP disease activity states in axSpA patients. ASAS HI and ASDAS-CPR were obtained from 140 consecutive axSpA patients, divided in the four ASDAS-CRP disease activity categories. High and very high disease activity were considered together. The ASAS HI cut-offs were obtained from the arithmetic mean, rounded off to the closest whole number, of the 75th percentile mean value of a lower rank and the 25th percentile mean value of the adjacent higher rank. This approach was applied in the transition from inactive disease and moderate disease activity, and in the transition from moderate disease activity and high/very high disease activity. Twenty-three patients were classified as having inactive disease, 36 were classified as having moderate disease activity, and 81 were in a high/very high disease activity state. Using the approach of the 75th-25th percentile mean values of adjacent disease activity states, the ASAS HI cut-offs resulted: ≤4 to dinstinguish a normal functioning, >4 and ≤8 to distinguish a moderate impairment of functioning, and >8 to distinguish a severe impairment of functioning. ASAS HI seems a reliable tool to define functioning categories in patients with axSpA.