Dynamic lactate dehydrogenase/lymphocyte ratio and C-reactive protein as predictors of mortality after plasma exchange in ANCA-associated vasculitis: A retrospective case control study.

The efficacy of plasma exchange (PLEX) in anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV) remains controversial. Early identification of patients unlikely to benefit from PLEX could optimize immunosuppressive strategies. We investigated whether dynamic changes in the lactate dehydrogenase-to-lymphocyte ratio and C-reactive protein (CRP) levels predict in-hospital mortality among critically ill AAV patients undergoing PLEX. In this retrospective, single-center cohort study, 33 adult AAV patients treated with ≥3 PLEX sessions between January 2010 and June 2021 were included. Biochemical parameters were measured immediately before the first and after the final PLEX session. Univariate comparisons between survivors and non-survivors employed Mann-Whitney U and chi-square tests as appropriate. A classification and regression tree (CART) model was constructed, following variable selection, variance inflation factor, and recursive feature elimination, to identify key mortality predictors. Model performance was assessed by the area under the curve (AUC) and cross-validation. Median age was 55 years (range 20-83); 57.6% were male. In-hospital mortality was 39.4% (n = 13). Non-survivors exhibited significantly greater post-PLEX increases in LDH/Ly (median 1.1 vs 0.3; P < .001) and higher final CRP levels (median 10.2 vs 2.8 mg/L; P = .008). The CART model identified post-PLEX LDH-lymphocyte ratio >0.55 as the primary discriminator for mortality, with secondary stratification by CRP > 0.67 mg/dL. The model achieved AUCs of 0.89 (training) and 0.71 (test). Dynamic assessment of LDH-lymphocyte ratio and CRP after PLEX may serve as early, readily available predictors of mortality in critically ill AAV patients. These findings warrant validation in larger, prospective cohorts to refine patient selection for PLEX and tailor adjunctive therapies.