Findings presented at the European League Against Rheumatism (EULAR) Congress 2017, held in Madrid, Spain, show that serum amyloid A (SAA) levels were significantly correlated with C-reactive protein (CRP) levels in psoriatic arthritis, suggesting repeated SAA measurements could act as an additional marker for monitoring disease activity over time in patients with psoriatic arthritis.
T. Martins Rocha, from Saint John Hospital in Porto, Portugal and colleagues included 53 patients from their rheumatology department who had psoriatic arthritis (according to Classification Criteria for Psoriatic Arthritis [CASPAR] criteria) and at least 1 SAA measurement between January 2015 and December 2016 in an observational retrospective study.
Of the 53 participants, 31 (59%) were women with a mean (SD) age of 50 (11.2) years and a median disease duration of 9 years; 28% had axial involvement, 34% had peripheral involvement, and 38% had both. All patients were being treated with biologic disease-modifying antirheumatic drugs. Demographic and clinical data were obtained with the national database (Reuma.pt). The researchers measured the difference in all variables (median time between measurements of the variables in patients was 6 months).
The researchers found that median SAA and erythrocyte sedimentation rate (ESR) levels were significantly superior in women (23 vs 6 mm/first hour, and 8.6 vs 4.4 mg/L, respectively; P <.05), and that only ESR levels correlated with age (r=0.20; P =.05).
The 3 biomarkers, SAA, ESR, and CRP, showed a weak association with serum creatinine levels. SAA showed greater correlation than the other two (r=0.46; P <.001). SAA levels had a stronger correlation with CRP (r=0.75; P <.001) than with ESR levels (r=0.26; P <.01).
SAA and CRP (dichotomized as negative/positive) had a greater level of agreement (κ=0.40) compared with ESR (κ=0.26 and κ=0.32, respectively).
The researchers found no significant correlations between the biomarkers and the tender/swollen joint count or the pain/global disease activity visual analogue scale.
SAA levels correlated with Ankylosing Spondylitis Disease Activity Score (ASDAS) CRP (r=0.43; P <.001), and weakly correlated with ASDAS ESR and 28-joint Disease Activity Score (DAS28) CRP (r= 0.20 and r=0.24, respectively; P <.05).
Only ESR had significant weak correlations with Bath Ankylosing Spondylitis Disease Activity Index, Maastricht Ankylosing Spondylitis Enthesitis Score, and Spondyloarthritis Research Consortium of Canada scores (r=0.25, r=0.21, r=0.35, respectively; P <.05).
All the biomarkers had weak correlations with Bath Ankylosing Spondylitis Functional Index and Health Assessment Questionnaire scores.
ΔSAA levels had a weak correlation with ΔCRP (r=0.32; P =.03; n=47), and no significant association was found with ΔESR. ΔSAA correlated significantly with ΔASDAS CRP and ΔBath Ankylosing Spondylitis Metrology Index (r=0.32 and r=0.39; P <.05).
“SAA levels and its variation had a significant correlation with CRP levels and its variation, respectively. Significant association with ASDAS CRP variations suggests that serial measurements of SAA may represent an additional marker for monitoring disease activity over time in [patients with psoriatic arthritis],” the researchers concluded.
Rocha TM, Fonseca R, Rosa-Goncalves D, et al. Serum amyloid A levels as a potential biomarker to monitor psoriatic arthritis patients on biologics — a retrospective observational study. Presented at: European League Against Rheumatism (EULAR) Congress 2017; June 14-17, 2017; Madrid, Spain. Abstract THU0690. doi:10.1136/annrheumdis-2017-eular.5466