Inflammatory blood count ratios discriminate disease activity and remain persistently elevated during glucocorticoid-free remission in ANCA-associated vasculitis.

Inflammatory ratios derived from routine complete blood counts, including the neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and monocyte-to-lymphocyte ratio (MLR), have been proposed as activity markers in ANCA-associated vasculitis (AAV), but their interpretation is limited by heterogeneous sampling and treatment-related confounding. We conducted a single-center cross-sectional study including adult patients with granulomatosis with polyangiitis (GPA) or microscopic polyangiitis (MPA). Patients were sampled during active disease (new-onset prior to induction or relapse prior to escalation) or during stringent glucocorticoid-free remission (BVASv3 = 0). Healthy controls (HCs) were included for secondary comparisons. Ratios were compared across groups and correlated with BVASv3 and c-reactive protein (CRP). Between-group differences (active vs. remission; remission vs. healthy controls) were additionally quantified using age- and sex-adjusted log-linear models (log-transformed outcomes), reported as ratios of geometric means. Discriminative performance for active disease versus remission was assessed using unadjusted ROC analyses and age- and sex-adjusted logistic regression models. Sensitivity analyses stratified remission by maintenance immunosuppression at sampling. The study included 99 AAV patients (28 active, 71 remission) and 258 HCs. NLR, PLR, and MLR were significantly higher in active disease than in remission (all p ≤ 0.004), and remained significantly higher after age/sex adjustment in log-linear models (geometric mean ratios [Active/Remission]: NLR 1.97, PLR 1.64, MLR 1.40). NLR and PLR correlated moderately with BVASv3 (ρ = 0.506 and 0.478, respectively; both p < 0.001) and CRP. Discriminative performance was strongest for NLR and PLR: in age- and sex-adjusted models, AUC increased from 0.664 (age/sex only) to 0.832 after adding NLR and 0.827 after adding PLR (whereas the AUC after adding MLR was 0.724). During glucocorticoid-free remission, ratios remained higher than in HCs (geometric mean ratios: NLR 1.55 [1.39-1.74], PLR 1.18 [1.08-1.29], MLR 1.40 [1.27-1.55]; all p < 0.001). Treatment stratification within remission showed lower lymphocyte counts and higher PLR in patients on maintenance immunosuppression, while NLR discrimination remained robust across strata. Routine blood count-derived inflammatory ratios, particularly NLR and PLR, discriminate active AAV from stringent glucocorticoid-free remission independent of age/sex, and remain persistently altered during remission. These inexpensive and widely available indices may complement clinical assessment, warranting prospective validation and evaluation of prognostic value.