Hypoalbuminaemia in antineutrophil cytoplasmic antibody-associated vasculitis: incidence and significance

Objective Hypoalbuminaemia has been proved to be a biomarker of poor prognosis in many diseases. The objective of this study was to investigate the significance of hypoalbuminaemia in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). Methods Data of 117 AAV patients were analysed retrospectively. The relationship between hypoalbuminaemia and disease severity were studied. The influence of albumin on the pathogenetic role of ANCA was investigated in vitro. Results Among all patients, 52 had light hypoalbuminaemia (30g/L<=albumin<35g/L) and 40 had nephrotic hypoalbuminaemia (albumin <30g/L). Patients with hypoalbuminaemia had higher inflammation levels and more severe kidney injury than patients without hypoalbuminaemia, but no significant difference of the urinary protein levels were found between patients with nephrotic and light hypoalbuminaemia. Multivariate analysis showed serum albumin correlated with age (r=-0.566, p=0.018), C-reactive protein (r=-0.521, p=0.032) and haemoglobin (r=0.512, p=0.036). Patients with nephrotic hypoalbuminaemia had higher incidence of infection, end stage renal disease and all cause mortality during treatment than patients with light hypoalbuminaemia or normal serum albumin. In vitro study indicated albumin could inhibit the binding between ANCA and neutrophils in a concentration dependent manner. Albumin also inhibited the ANCA-induced respiratory burst and neutrophil extracellular traps formation. Conclusion Serum albumin have an inhibitory effect on the binding between ANCA and its antigen. The incidence of hypoalbuminaemia in AAV with kidney involvement is high but is not caused by heavy proteinuria. Hypoalbuminaemia is correlated with the high inflammation level and poor prognosis of AAV. Therapy targeting hypoalbuminaemia might benefit patients with AAV.