Correlations between serum acute-phase protein SAA, platelet-to-lymphocyte ratio, and disease activity in ankylosing spondylitis

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.

To investigate the clinical value of serum amyloid A (SAA) and platelet-to-lymphocyte ratio (PLR) in assessing disease activity in patients with AS.

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.

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).

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.