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

Abstract

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 +/- 7.49mg/L versus 2.73 +/- 1.57mg/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.

Fig. 1

Comparison of SAA levels between patients with AS and controls. The mean SAA level of patients with AS was significantly higher than that of controls (9.52 ± 7.49 mg/L versus 2.73 ± 1.57 mg/L, p < 0.05). The horizontal bar represents the mean SAA value of each group.

Fig. 2

Correlation of SAA levels with BASDAI scores, ESR and CRP levels, and the correlation between ESR and CRP levels in patients with AS. (A) SAA levels correlated well with BASDAI scores (r = 0.431, p = 0.007). (B) SAA levels correlated well with ESR (r = 0.521, p = 0.001). (C) SAA levels correlated well with CRP levels (r = 0.648, p < 0.001). (D) ESR correlated well with CRP levels (r = 0.703, p < 0.001).

Fig. 3

Correlation of SAA levels with BASDAI scores in patients with a normal ESR and CRP levels. A. SAA levels showed a trend of positive correlation with BASDAI scores in patients with a normal ESR (r = 0.460, p = 0.073). B. SAA levels showed a trend of positive correlation with BASDAI scores in patients with normal CRP levels (r = 0.486, p = 0.185).