Low copy number (CN) of the FCGR3B gene reduces FCGR3B membrane expression on neutrophils and results in clearance of a smaller amount of immune complex. We investigated FCGR3B CN in relation to the clinical phenotype in a Caucasian SLE cohort (). FCGR3B CN was determined by three different qPCR parameter estimations (Ct−, Cy0, and cpD1) and confirmed by the FCGR2C/FCGR2A paralog ratio test. Clinical and serological data were then analyzed for their association with FCGR3B CN. Low FCGR3B CN (2). In multivariate analyses, LN was independently associated with anti-C1q-Ab levels () and low FCGR3B CN (). We conclude that the susceptibility for LN in patients with low FCGR3B CN is linked to increased levels of pathogenic autoantibodies.