Neutrophil-to-Lymphocyte and Platelet-to-Lymphocyte Ratios in Psoriatic Arthritis: A DAPSA-Based Validation Study.

OBJECTIVES: Neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) are accessible markers of systemic inflammation. Their potential use as indicators of disease activity in psoriatic arthritis (PsA) remains unclear. This study aimed to validate NLR and PLR as markers of PsA activity using the Disease Activity in Psoriatic Arthritis (DAPSA) score as reference. METHODS: This retrospective observational study included 426 PsA patients, with disease activity available for 102. Demographic, clinical, and laboratory data were retrieved from electronic records. Disease activity was assessed using DAPSA, with remission defined as ≤4 and active disease as ≥5. Discriminatory capacity was evaluated using receiver operating characteristic (ROC) curve analysis, including area under the curve (AUC), sensitivity, specificity, and predictive values. RESULTS: Among the 102 patients with available DAPSA data, 39.2% were in remission and 60.8% had active disease. Mean NLR and PLR were 1.8 ± 0.6 and 104.5 ± 31.2 in remission versus 2.3 ± 2.8 and 134.7 ± 106.6 in active PsA (p = 0.311 and p = 0.081, respectively). ROC analysis showed poor discriminatory capacity for NLR (AUC 0.542, 95% CI 0.43-0.66, p = 0.47, sensitivity 68%, specificity 48%) and modest for PLR (AUC 0.604, 95% CI 0.50-0.71, p = 0.08, sensitivity 52%, specificity 57%), with optimal cut-offs of 1.55 and 111.1, respectively. CONCLUSIONS: NLR and PLR did not demonstrate sufficient validity as independent tools for classifying disease activity in PsA compared to DAPSA. Although their simplicity makes them attractive for clinical use, their diagnostic accuracy for PsA appears limited.