Serum Glial Fibrillary Acidic Protein Can Predict Cross-Sectional Vasculitis Activity by Reflecting Renal Involvement in Patients with Antineutrophil Cytoplasmic Antibody-Associated Vasculitis

<i>Background and Objectives:</i> Glial fibrillary acidic protein (GFAP) is a type III intermediate filament protein primarily produced by cells in the central nervous system (CNS) and other major organs such as the kidneys. This study investigated whether serum GFAP could be used to estimate cross-sectional vasculitis activity presented via the Birmingham vasculitis activity score (BVAS) in patients with antineutrophil cytoplasmic antibody-associated vasculitis (AAV). <i>Materials and Methods:</i> This study included 74 patients with AAV. Clinical and laboratory data at diagnosis including BVAS and C-reactive protein (CRP) were reviewed. During follow-up, all-cause mortality and end-stage kidney disease (ESKD) were considered poor outcomes. Serum GFAP was measured from sera collected and stored at diagnosis. <i>Results:</i> The median age of the 74 patients was 63.5 years. Serum GFAP was inversely correlated with the cross-sectional BVAS (r = -0.373) and CRP (r = -0.320). It was also significantly correlated with general (r = -0.237) and renal (r = -0.335) manifestations among BVAS systemic items, and furthermore, among minor items of renal manifestation, correlating with sum scores for proteinuria (r = -0.409) and haematuria (r = -0.305). Additionally, compared with patients with serum GFAP > 194.9 pg/mL, those with serum GFAP ≤ 194.9 pg/mL showed a higher risk for progression to ESKD (relative risk 3.150) and a significantly lower cumulative ESKD-free survival rate. <i>Conclusions:</i> This study demonstrated the clinical potential of serum GFAP at diagnosis for predicting not only cross-sectional vasculitis activity through the anticipation of the extent of renal involvement but also future progression to ESKD in patients with AAV.