Performance of the Ankylosing Spondylitis Disease Activity Score based on a quick quantitative C-reactive protein assay in patients with axial spondyloarthritis.

Abstract

To evaluate the performance of the Ankylosing Spondylitis Disease Activity Score based on a validated quick quantitative C-reactive protein assay (ASDAS-qCRP) as compared to ASDAS based on a routine lab CRP assay (ASDAS-CRP) and ASDAS based on erythrocyte sedimentation rate (ASDAS-ESR). Disease activity assessment was performed in 50 patients with axial spondyloarthritis (axSpA). Routine lab CRP was measured in the central lab while the quantitative quick-CRP assay and ESR measurements were performed locally. ASDAS-CRP, ASDAS-qCRP and ASDAS-ESR were subsequently calculated. The mean (±SD) serum level of the routine lab CRP (6.2±8.3mg/l) was lower than of the quick-CRP (7.4±8.4mg/l) (P<0.05). Whereat, there was no significant difference in the mean values of ASDAS-CRP and ASDAS-qCRP in axSpA patients (2.70±0.94 and 2.74±0.96, respectively, P=0.069), while the ASDAS-ESR (2.85±1.0) was significantly higher than ASDAS-CRP (P=0.036) and numerically higher than ASDAS-qCRP (P=0.125). In 47 of the 50 cases of axSpA (94%), patients were assigned to the same disease activity category according to ASDAS-CRP and ASDAS-qCRP. ASDAS-qCRP performed similarly well compared to ASDAS-CRP with the absolute agreement on the disease activity category according to the ASDAS of 94%. ASDAS-qCRP is, therefore, feasible for an immediate decision-making in clinical practice and trials aimed at treating to target.