ASDAS high disease activity versus BASDAI elevation in patients with ankylosing spondylitis as selection criterion for anti-TNF therapy

Objective: To investigate which of the 2 ankylosing spondylitis (AS) disease activity instruments identifies better those patients with characteristics that have been associated with positive response to anti-TNF therapy.

Methods: Data from patients with AS in the REGISPONSER registry were analyzed. Patients were categorized by disease activity using 3 different selection criteria: elevated Bath Ankylosing Spondylitis Disease Activity Index criteria (BASDAI≥4), high Ankylosing Spondylitis Disease Activity Score (ASDAS≥2.1), or very high ASDAS (ASDAS≥3.5). To determine which criterion selects for patients most likely to respond to anti-TNF therapy, the groups of patients selected with each criterion were compared on five disease characteristics that are associated with good response to anti-TNF therapy: lower age, lower function score, less enthesitis, higher C-reactive protein (CRP), and HLA-B27-positive status.

Results: 50.9%, 66.3%, and 24.9% of 1156 patients had elevated BASDAI, high ASDAS, or very high ASDAS, respectively. Compared to patients selected with elevated BASDAI, more patients selected with high ASDAS had characteristics associated with good response to anti-TNF therapy. Patients with very high ASDAS had higher CRP and were younger, but more frequently had enthesitis and had higher function scores when compared to those with elevated BASDAI.

Conclusions: Selection of AS patients with the ASDAS instrument results in patient sub-populations with different characteristics than those selected with the BASDAI instrument. Since some of these characteristics have been associated with response to anti-TNF therapy, further study should establish if the choice of selection instrument improves the outcome of therapy in the selected populations.