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of CRP or ESR). The cutoffs between the disease activity states are: inactive disease
≤1.3, moderate 1.3–2.0, high 2.1–3.5, and very high ≥3.5. The ASDAS cutoff for
clinically important improvement between examinations is ≥1.1 and the cutoff for
a major improvement is ≥2.0. The ASDAS has been extensively validated. It has
been shown to be reliable, discriminative, and sensitive [ 27 – 29 ].
Physical Function (BASFI, DFI, HAQ-S)
Limited spinal mobility and decrease in function is a major and also clinically a
poor prognostic sign of axial SpA. Consequently, physical function is considered as
a major outcome for patients with SpA. Patients with AS report signifi cantly
impaired health on all scales of the Short Form (SF-36) as compared to the general
population or patients with other medical conditions. Patients with AS also have
rather low scores in physical domains [ 30 ]. Studies have shown an association
between spinal mobility measures and radiographic damage in patients with AS [ 31 ,
32 ]. However, physical function in patients with AS is infl uenced not only by struc-
tural damage but also by disease activity (infl ammation) [ 32 , 33 ]. It is important to
realize that the term “function” is frequently limited to physical function in this
context, ignoring the complexity of global functioning. However, the infl uence of
other factors, such as psychological factors, has only rarely been studied in AS.
Bath Ankylosing Spondylitis Functional Index
The most frequently used tool to asses function in axial SpA is the BASFI (Bath
Ankylosing Spondylitis Functional Index) , which measures the functional status as
a self-report. It contains ten questions on activities of daily living, which are scored
with a rating scale from 0 (no functional impairments) to ten (maximal impairment)
[ 34 ]. Domains addressed in the questionnaire are:
- Bending
- Reaching
- Getting up
- Putting on socks
- Climbing stairs
- Looking over the shoulder
The mean of the individual scores is calculated to give the overall index score.
The sum score ranges from 0 to 10, with higher values indicating worse functioning.
The MCID has been reported at 7 mm or change of 17.5 % with a sensitivity of 0.60
and a specifi city of 0.85 [ 20 ]. The BASFI is reliable, sensitive to change, and fea-
sible to use in patients with AS in clinical practice. However, since the median score
of the BASFI has been reported as 2.0 with clustering at the lower end of the scale,
the questionnaire may not be suffi ciently sensitive to detect changes in functioning
in patients without severe impairments.
U. Kiltz et al.