This retrospective cross-sectional observational study aims to evaluate the association between the C-reactive protein-albumin-lymphocyte (CALLY) index and disease activity and functional status in patients with ankylosing spondylitis. Medical records of adult patients followed between January 1, 2022, and December 31, 2025, were reviewed. Disease activity was assessed using BASDAI and ASDAS-ESR, and functional status was evaluated using BASFI. The study investigates whether the CALLY index reflects systemic inflammatory burden beyond patient-reported disease activity

Ankylosing spondylitis is a chronic inflammatory disease in which assessment of disease activity may require both clinical and laboratory-based measures. This retrospective cross-sectional observational study was conducted at Bursa City Hospital, Türkiye, to investigate the relationship between the C-reactive protein-albumin-lymphocyte (CALLY) index and disease-related parameters in patients with ankylosing spondylitis.

Medical records of patients aged 18 years and older who met the modified New York criteria for ankylosing spondylitis and were followed between January 1, 2022, and December 31, 2025, were retrospectively reviewed. Patients with active or chronic infection, malignancy, advanced hepatic or renal disease, nephrotic syndrome, or incomplete data were excluded.

Demographic, clinical, and laboratory data were obtained from medical records. Disease activity was assessed using the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and the Ankylosing Spondylitis Disease Activity Score based on erythrocyte sedimentation rate (ASDAS-ESR). Functional status was evaluated using the Bath Ankylosing Spondylitis Functional Index (BASFI). The CALLY index was calculated using serum C-reactive protein, albumin, and lymphocyte count values.

The primary objective of the study is to determine whether the CALLY index is associated with disease activity and functional status in ankylosing spondylitis. The study also aims to explore whether this composite biomarker reflects systemic inflammatory burden beyond subjective patient-reported measures. Ethical approval was obtained from the Bursa City Hospital Clinical Research Ethics Committee.

Inclusion Criteria:

• Age 18 years and older
• Diagnosis of ankylosing spondylitis according to the modified New York criteria
• Availability of complete clinical and laboratory data at a single assessment time point

Exclusion Criteria:

• Active or chronic infection
• Malignancy
• Advanced hepatic or renal disease
• Having conditions affecting serum albumin levels, such as nephrotic syndrome
• Incomplete data

Adult patients with ankylosing spondylitis who were followed at Bursa City Hospital, Türkiye, and whose medical records were retrospectively reviewed between January 1, 2022, and December 31, 2025.