Complete blood count-derived biomarkers as indicators of systemic lupus erythematosus activity: a cross-sectional comparative study

Background SLE is a chronic autoimmune disease with heterogeneous manifestations. This study evaluated the discriminative value of complete blood count-derived biomarkers, including neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), monocyte-to-lymphocyte ratio (MLR), eosinophil-to-lymphocyte ratio (ELR), basophil-to-lymphocyte ratio (BLR), mean platelet volume and red cell distribution width (RDW), in identifying lupus flares. Methods This cross-sectional study was conducted over 10 years in the internal medicine department of Sahloul Hospital. SLE patients were classified by disease activity using Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2K): flare (SLEDAI-2K >6) or remission (SLEDAI-2K ≤6). A matched group of healthy controls was included. Comparisons were made between flare/remission and flare/controls. Discriminative performance of biomarkers was evaluated using receiver operating characteristic analysis, with sensitivity (Se), specificity (Sp) and area under the curve (AUC) determined for the optimal cut-off values. Results The study included 83 SLE patients (40 flares, 43 remission) and 85 controls, median age of 32 years and a sex ratio of 0.16. Compared with remission, flares had significantly higher NLR and RDW and lower ELR. The most discriminative biomarkers were RDW (AUC=0.708, cutoff ≥14.65, Se =75.9%, Sp =60.6%), NLR (AUC =0.636, cutoff ≥2.63, Se =72.4%, Sp =51.5%) and ELR (AUC =0.647, cutoff ≤0.0076, Se =74.4%, Sp =65%). Compared with controls, flares showed higher NLR, PLR, MLR, RDW and lower ELR and BLR. Best performances were RDW (AUC =0.864, cutoff ≥13.85, Se =89.7%, Sp =75.3%), NLR (AUC =0.822, cutoff ≥2.28, Se =79.3%, Sp =76.5%) and ELR (AUC =0.775, cutoff ≤0.029, Se =87.1%, Sp =70.3%). SLEDAI-2K correlated positively with NLR (r =0.228), PLR (r =0.238), RDW (r =0.303) and negatively with ELR (r =–0.317). Conclusions These biomarkers may serve as simple, accessible and cost-effective tools for detecting lupus flares, particularly in resource-limited settings.