The CALLY Index May Reflect Systemic Inflammatory Burden Rather than Patient-Reported Disease Activity in Ankylosing Spondylitis: A Medical Record-Based Cross-Sectional Study

Background: Ankylosing spondylitis (AS) is a chronic inflammatory disease in which accurate assessment of disease activity remains challenging. Although composite indices such as BASDAI and ASDAS are widely used, they may not fully capture systemic inflammatory burden. The C-reactive protein–albumin–lymphocyte (CALLY) index is an emerging composite biomarker integrating inflammatory, nutritional, and immunological components. This study aimed to evaluate the association of the CALLY index with disease activity, functional status, and quality of life in AS. Methods: This medical record-based cross-sectional study included 65 patients with AS. Disease activity was assessed using BASDAI and ASDAS-ESR, functional status using BASFI, and quality of life using the 12-Item Short Form Health Survey (SF-12). The CALLY index was calculated from serum CRP, albumin levels, and lymphocyte counts. Correlation and multivariable linear regression analyses were performed. Results: The mean CALLY index was 58.43 ± 66.20. The index showed moderate negative correlations with ESR and ASDAS-ESR and a positive correlation with lymphocyte count. Its strong inverse correlation with CRP was expected because CRP is part of the formula and was therefore interpreted cautiously. No significant associations were found with BASDAI, BASFI, or SF-12. In multivariable analysis, BMI (β = −0.299, p = 0.012) and NSAID use (β = −0.298, p = 0.011) were independent predictors. Conclusions: The CALLY index was associated mainly with objective inflammatory markers rather than patient-reported outcomes, suggesting a dissociation between biochemical and clinical disease domains in AS. These findings are preliminary and require confirmation in larger longitudinal studies before clinical application.