Clinical, serological, and hematological profiles according to age at diagnosis in primary Sjögren disease: a single-center cross-sectional study

Primary Sjögren disease (pSjD) is a systemic autoimmune disease with heterogeneous clinical, serological, and hematological manifestations. Because symptom onset and diagnostic delay may be difficult to determine retrospectively, age at diagnosis may provide a pragmatic framework for describing clinical heterogeneity. This study compared clinical, serological, and hematological profiles across diagnosis-age groups in pSjD. This retrospective cross-sectional study included 258 patients with definite primary Sjögren disease fulfilling the 2016 ACR/EULAR classification criteria after exclusion of cases with uncertain primary/secondary status. Patients were stratified according to age at diagnosis into young-adult (< 40 years, n = 54), middle-age (40–59 years, n = 137), and late (≥ 60 years, n = 67) groups. Demographic, clinical, serological, hematological, and composite inflammatory indices were compared. Logistic regression was used to evaluate exploratory sex-adjusted associations with pulmonary involvement. ROC analysis was performed to evaluate the modest discriminative performance of RDW-SD for late versus young-adult diagnosis-age groups. Pulmonary involvement was observed in 2/54 (3.7%) young-adult, 7/137 (5.1%) middle-age, and 19/67 (28.4%) late diagnosis-age patients (p < 0.001). In exploratory sex-adjusted logistic regression, late diagnosis-age was associated with pulmonary involvement compared with young-adult diagnosis-age (OR 8.20, 95% CI 1.75–38.32), whereas middle-age diagnosis was not (OR 1.34, 95% CI 0.26–6.83). Extraglandular involvement also differed across groups (31.5%, 16.8%, and 35.8%, respectively; p = 0.006). Corticosteroid exposure was more frequent in the late diagnosis-age group (7.4%, 18.2%, and 32.8%; p = 0.002), but was interpreted as a treatment variable rather than an intrinsic disease phenotype. CRP, neutrophil count, monocyte count, RDW-SD, NLR, SIRI, SII, and AISI differed across groups. RDW-SD showed only modest discriminatory ability for late versus young-adult diagnosis-age groups (AUC 0.645, 95% CI 0.538–0.746). Autoantibody profiles were broadly comparable, although anti- SSB/La positivity was more frequent in the young-adult group. In this single-center cohort, age at diagnosis was associated with differences in selected clinical and hematological characteristics in pSjD. Late diagnosis-age was associated with a higher frequency of clinically recognized pulmonary involvement; however, this finding should be interpreted cautiously because smoking data were incomplete, HRCT screening was not systematic, age-related comorbidities were more common in older patients, and reverse causality related to ILD workup cannot be excluded. RDW-SD should be considered an exploratory CBC-derived marker with modest performance rather than a clinically established biomarker.