The Usefulness of White Blood Cell Inflammatory Parameters in Children With Systemic Lupus Erythematosus

To evaluate the utility of novel parameters related to immune cell activation, known as white blood cell parameters of inflammation (WBC-IP), as biomarkers of disease activity in childhood-onset systemic lupus erythematosus (cSLE) and compare their performance with conventional markers, including erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and procalcitonin (PCT).

We conducted a cross-sectional analysis, including patients with cSLE with active disease (n = 43), remission (n = 31), and healthy controls (n = 112). In a separate longitudinal cohort, patients with active cSLE at baseline were reassessed after four to six weeks and when achieving inactive disease. WBC-IP was measured in dipotassium EDTA-anticoagulated tubes using the Sysmex XN-Series analyzer. Associations with SLEDAI-2K, clinical SLEDAI-2K, and physician global assessment (PGA) scores were assessed using Spearman's rank correlation. Diagnostic performance for distinguishing active disease from remission was evaluated by the area under the receiver operating characteristic curve (AUC).

Significant alterations in neutrophil- and lymphocyte-related parameters were observed across disease states. The proportion of immature granulocytes (IG%) correlated most strongly with the SLEDAI-2K (r_s = 0.51), clinical SLEDAI-2K (r_s = 0.50), and PGA (r_s = 0.57; all P < 0.0001) and showed comparable associations with ESR, CRP, and PCT. Longitudinal changes in IG%, neutrophil reactivity intensity, and lymphocyte complexity indices paralleled improvements in disease activity. IG% best discriminated active cSLE among WBC-IP (AUC 0.90, 95% confidence interval [CI] 0.83-0.98; cutoff >0.35, sensitivity 81.4%, specificity 87.1%), whereas ESR demonstrated the highest AUC among conventional markers (AUC 0.92, 95% CI 0.85-0.99).

Among the WBC-IP evaluated, IG% showed the strongest association with disease activity and demonstrated diagnostic performance comparable to that of ESR, suggesting it may represent a potential biomarker of disease activity. Further validation in independent cohorts is warranted.