Patients at high risk of IVIG-associated hemolysis (defined as receipt of a 28-day cumulative dose of ≥ 2 g/kg, adjusted for ideal body weight, and non-O blood group) will be prospectively monitored using a standardized protocol for signs of hemolysis, and will be undergo additional testing for variables that have been hypothesized to increase the risk of hemolysis. The goal of the study is to define the incidence and dynamics of IVIG-mediated hemolysis and identify patient and product-related factors that may predict which patients are especially at risk.