Hypocomplementemia C3 and anti-SSB positivity: associated factors and a predictive model for hematological involvement in Sjögren’s disease

Objective Hematological involvement occurs in over 20% of patients with Sjögren’s disease (SjD), yet its associated factors remain poorly characterized. This retrospective cross-sectional study aimed to evaluate clinical and immunological factors associated with concurrent hematological involvement in SjD using blood cell damage stratification. Methods A total of 163 hospitalized SjD patients without recent high-dose glucocorticoids or potent immunosuppressants (2018–2024) were enrolled. Demographic data, clinical characteristics, laboratory parameters, and disease activity indices were collected. Patients were classified into two groups based on the presence or absence of baseline hematological involvement. Multivariable logistic regression identified factors independently associated with concurrent hematological involvement and constructed a cross-sectional classification model. The model’s discriminative performance was evaluated using receiver operating characteristic (ROC) curves, calibration plots, and decision curve analysis (DCA). Results Among 163 enrolled SjD patients, 70 (42.9%) had hematological involvement, while 93 (57.1%) did not. Compared with patients without hematological involvement, those with involvement had significantly higher levels of globulin (median 40 vs. 33 g/L), IgG (median 18.0 vs. 15.5 g/L), and modified ESSDAI scores (excluding the hematological domain, median 9.0 vs. 6.0), as well as lower C3 (median 0.74 vs. 0.86 g/L) and C4 levels (median 0.16 vs. 0.18 g/L) (all P < 0.05). Patients with multilineage cytopenia exhibited elevated IgG levels, increased disease activity, higher anti-SSB positivity rates, and reduced C3 levels. C3 hypocomplementemia (OR 0.21, 95% CI 0.02–2.67, P < 0.05) and anti-SSB positivity (OR 6.61, 95% CI 1.59–110, P < 0.05) were independently associated with concurrent hematological involvement. The combined model incorporating C3 and anti-SSB antibody yielded an AUC of 0.741 (95% CI: 0.642–0.841), outperforming either C3 (AUC = 0.633) or anti-SSB antibody (AUC = 0.656) when used alone. At the optimal cut-off value, the sensitivity and specificity were 76.7% and 68.4%, respectively. Conclusion C3 hypocomplementemia and anti-SSB positivity are independently associated with hematological involvement in SjD, and their combination may serve as a preliminary cross-sectional tool for identifying such patients at initial evaluation, pending external validation. Routine C3 and anti-SSB measurement may be a useful, accessible marker for raising suspicion of cytopenia in clinical practice.