MBL2 and lupus nephritis: In Danish laboratories, a p-MBL level ≤500 μg/l is defined as insufficient, and this is in agreement with the cut-off value used in previous studies investigating the impact of p-MBL levels in diseases such as severe acute respiratory syndrome coronavirus infection, chronic obstructive lung disease, systemic lupus erythematosus (SLE) and lupus nephritis (Ip et al., 2005; Eagan et al., 2010; Albert et al., 2012; Perazzio et al., 2016).