血清メトラル（Metrnl）はANCA関連血管炎における腎関与の潜在的バイオマーカー

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a systemic autoimmune disease with significant renal involvement. Identifying novel biomarkers for AAV, particularly for renal complications, remains a clinical priority. Metrnl, a recently identified cytokine with immunomodulatory properties, has been implicated in various inflammatory diseases, but its role in AAV is unknown.

This study investigated serum Metrnl levels in 37 patients with microscopic polyangiitis (MPA), 17 with granulomatosis with polyangiitis (GPA), and 30 healthy controls (HCs) using ELISA. Correlations with clinical parameters, including the Birmingham Vasculitis Activity Score (BVAS) and renal function indicators, were analyzed. Statistical analyses incorporated false discovery rate (FDR) correction for multiple comparisons.

Serum Metrnl levels were significantly elevated in both MPA and GPA patients compared to HCs. A strong positive correlation was observed between Metrnl levels and BVAS in both MPA and GPA subgroups. Crucially, Metrnl levels showed significant correlations with key renal impairment markers (creatinine, cystatin C, eGFR) after FDR adjustment. Furthermore, stratification of MPA patients by renal function (eGFR cut-off: 60 mL/min/1.73 m²) revealed substantially higher Metrnl levels in the impaired renal function group. Receiver operating characteristic (ROC) curve analysis indicated that Metrnl had superior diagnostic efficacy for identifying AAV with renal involvement (AUC = 0.8150) compared to diagnosing AAV overall (AUC = 0.7214).

This study provides the first evidence that serum Metrnl is elevated in AAV and is associated with disease activity and renal impairment. The strong association with renal dysfunction, robustly demonstrated by both correlation and stratification analyses, suggests Metrnl warrants further investigation as a potential biomarker for renal involvement in AAV.