Serum amyloid A as a useful indicator of disease activity in patients with ankylosing spondylitis

Purpose: To investigate whether serum amyloid A (SAA) levels are increased in patients with ankylosing spondylitis (AS) and whether its levels correlate well with AS disease activity. Materials and Methods: Thirty-eight patients with AS and 38 age- and sex-matched control subjects were enrolled in this cross-sectional study. Their SAA levels were quantitatively measured by immunonephelometry. An established, self-administered instrument for evaluating disease activity (Bath Ankylosing Spondylitis Disease Activity Index, BASDAI) was used to measure and acute phase reactants, including erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), in patients with AS. Results: Patients with AS had a significantly higher mean SAA level than controls (9.52 ± 7.49 mg/L versus 2.73 ± 1.57 mg/L, p < 0.05), and the mean BASDAI score of patients with elevated SAA levels was significantly higher than that of patients with normal SAA levels (5.6 ± 1.3 versus 4.4 ± 1.5, p < 0.05). SAA levels showed significant correlations with BASDAI scores (r = 0.431, p = 0.007), ESR (r = 0.521, p = 0.001) and CRP levels (r = 0.648, p < 0.001). Additionally, the correlation between ESR and CRP levels also appeared significant (r = 0.703, p < 0.001). In those with normal ESR or CRP levels, SAA levels and BASDAI scores were elevated (p < 0.05) and showed a trend of positive correlation with one another. Conclusion: Our data showed that SAA levels were increased in patients with AS and correlated well with disease activity. These findings suggest that SAA can be used as a valuable indicator of disease activity in AS.