Value of the Platelet-to-Lymphocyte Ratio and Platelet-to-Lymphocyte Product in the Evaluation of Systemic Lupus Erythematosus Disease Activity.

PURPOSE: This study aimed to evaluate the value of the platelet-to-lymphocyte ratio (PLR) and platelet-to-lymphocyte product (PLP) in assessing systemic lupus erythematosus (SLE) disease activity. METHODS: This retrospective, single-center study extracted clinical data from the electronic medical records of 418 participants. Disease activity was assessed using Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI 2000) and SLE Disease Activity Score (SLE-DAS). RESULTS: In the overall cohort, PLR showed no correlation with SLEDAI 2000 (ρ = 0.041, P = 0.409) or SLE-DAS (ρ = -0.020, P = 0.693). However, among patients with normal platelet counts, PLR positively correlated with SLEDAI 2000 (ρ = 0.169, P = 0.003) and SLE-DAS (ρ = 0.238, P < 0.001), whereas no such association was observed in those with thrombocytopenia. Conversely, PLP showed a significant negative correlation with SLEDAI 2000 (ρ = -0.278, P < 0.001) and SLE-DAS (ρ = -0.378, P < 0.001), and these associations persisted regardless of platelet counts. Multiple linear regression showed that PLP was independently associated with SLEDAI 2000 (B = -0.004, P = 0.049) and SLE-DAS (B = -0.010, P = 0.005). Moreover, PLP was independently associated with glucocorticoid dose grading (ρ = -0.285, P < 0.001). For identifying moderate-to-severe disease activity (SLE-DAS score >7.64), PLP showed an area under the curve (AUC) of 0.698 (95% confidence interval [CI]: 0.642 to 0.754), with 82.3% sensitivity and 55.0% specificity, outperforming platelet (AUC = 0.638, 95% CI: 0.581 to 0.694) and lymphocyte (AUC = 0.652, 95% CI: 0.592 to 0.712) counts. CONCLUSION: PLP is a newly proposed biomarker that may assist with the clinical assessment of SLE disease activity. Due to the cross-sectional design, the findings should not guide treatment decisions. PLR is only associated with disease activity in patients with normal platelet counts and shows no association in those with thrombocytopenia.