Versatile performance edges of HBsAg Next assay in diagnosis and therapeutic monitoring of HBV infection

•HBsAgNx assay significantly enhances the stringency of HBsAg detection in ascertaining HBsAg loss during treatment or in spontaneous clearance to assess the functional cure.•The performance of this assay is superior in various phases of HBV infection including samples that exhibited prozone effect without compromising the clinical specificity.•It is amenable to cost-effective in-house neutralization to confirm low HBsAg levels.•Overall this assay can improve HBsAg detection in challenging spectrum of HBV infection and further refine the assessment of endpoints in functional cure. Background: HBsAg Next assay (HBsAgNx) claims improved detection of HBsAg. The aim was to investigate its performance in ascertaining HBsAg loss, ability to detect HBsAg in various phases of HBV infection, specificity and its amenability to in-house neutralization. Methods: Analytical sensitivity was investigated using NIBSC standard (3rd WHO-IS). For clinical performance, out of 91,962 samples tested for HBsAg (Qual-II), 512 samples consisting of 170 cases with evidence of HBsAg loss during treatment (n = 116) and without treatment (n = 54), acute-hepatitis B (n = 90) and acute exacerbation of chronic-hepatitis B (n = 41), acute-hepatitis A (n = 24) and acute-hepatitis E (n = 9) positive, HIV-1 positive (n = 20), non-HBV, HAV and HEV related acute-hepatitis (n = 81) and HBsAg prozone (n = 14) as well as in-house neutralization (n = 63) were included. Results: The calculated limit of detection (LOD) was 0.004 IU/mL. Of the 170 patients with apparent HBsAg loss, 18/116 (15.5%) among treated and 15/54 (27.7%) with spontaneous clearance were positive in HBsAgNx (p