Correlations between serum acute-phase protein SAA, platelet-to-lymphocyte ratio, and disease activity in ankylosing spondylitis
NingNing Yu, TaiZhe Wang, ZhiGang LiuAbstract
Background
Ankylosing spondylitis (AS) is a chronic inflammatory rheumatic disease characterized by sacroiliitis and spinal osteophyte formation that needs sophisticated testing to improve the accuracy of activity assessment and clinical decision-making.
Objective
To investigate the clinical value of serum amyloid A (SAA) and platelet-to-lymphocyte ratio (PLR) in assessing disease activity in patients with AS.
Methods
Using the bath ankylosing spondylitis disease activity index (BASDAI), 160 AS patients were categorized into 3 subgroups: low activity (BASDAI <4, n = 60), moderate activity (4≤ BASDAI <6, n = 50), and high activity (BASDAI ≥6, n = 50). Quantitative measurements included SAA concentrations and PLR values, with subsequent analysis of their relationship to disease progression. Diagnostic performance was evaluated with receiver operating characteristic (ROC) curve methodology.
Results
The high-activity group showed significantly elevated SAA (48.3 mg/L ± 9.1 mg/L) and PLR (164.5 ± 29.2) versus moderate- (SAA: 29.0 mg/L ± 8.2 mg/L; PLR: 138.4 ± 27.6) and low-activity groups (SAA: 14.3 [11.7–17.2] mg/L; PLR: 102.7 ± 22.2) (all P < 0.001). Both markers correlated strongly with BASDAI (SAA: r = 0.76; PLR: r = 0.71, P < 0.001). ROC analysis demonstrated that an SAA cutoff of 30.6 mg/L predicted high activity (96% sensitivity, 80% specificity), while PLR ≥143.7 showed 78.0% sensitivity and 76.4% specificity. Combined detection achieved superior area under the curve (0.95) versus individual markers (SAA: 0.93; PLR: 0.86).
Conclusion
SAA and PLR are strongly associated with BASDAI-defined disease activity in AS, and combined assessment improves identification of high disease activity, supporting their potential role as objective adjunctive markers in clinical assessment.