This systematic review identifies studies of limited quality reporting heterogeneous sepsis cohorts with varying lower limits of normal for IgG. Although our data suggest that a subnormal IgG measurement on the day of sepsis diagnosis does not identify a subgroup of patients with a higher risk of death, further studies are needed to confirm or refute this finding, and whether optimal cut-offs and time windows can be defined for IgG measurement. This would determine whether patients receiving intravenous immunoglobulin therapy for sepsis could be stratified using IgG levels.