Assessing disease activity in psoriatic arthritis (PsA) remains challenging, and additional biomarkers that can complement conventional inflammatory markers are still needed. The CRP-albumin-lymphocyte (CALLY) index integrates inflammatory, immune, and nutritional components into a single measure. This study examined the relationship between the CALLY index and disease activity in patients with PsA. This retrospective longitudinal cohort study included 150 patients with PsA and 50 age- and sex-matched healthy controls. Blood-derived inflammatory indices, including neutrophil-to-lymphocyte ratio (NLR), monocyte-to-lymphocyte ratio (MLR), platelet-to-lymphocyte ratio (PLR), systemic immune-inflammation index (SII), pan-immune inflammation value (PIV), and the CALLY index, were calculated using routine laboratory data. Disease activity was evaluated with the clinical Disease Activity Index for Psoriatic Arthritis (cDAPSA). Correlation analyses, receiver operating characteristic (ROC) analyses, subgroup analyses, and multivariable logistic regression models were performed. Patients with moderate-to-high disease activity had markedly lower CALLY index values than those with remission or low disease activity. The CALLY index showed a moderate inverse correlation with cDAPSA scores (r = - 0.529, p < 0.001). During follow-up, CALLY values increased significantly in both csDMARD-treated and biologic-treated patients (both p < 0.001), whereas no significant differences were observed between treatment groups. In multivariable analysis, lower log-transformed CALLY index values remained independently associated with moderate-to-high disease activity (OR 0.39, 95% CI 0.23-0.66). The discriminative performance of the CALLY index was similar to that of CRP (AUC 0.724 vs. 0.738; p = 0.42). Lower CALLY index values were linked to greater disease activity in PsA and improved alongside reductions in inflammatory burden during follow-up. Although its performance was comparable to CRP rather than superior, the CALLY index may represent a useful complementary biomarker for disease activity assessment in PsA. Prospective studies are needed to further clarify its clinical utility.
