Longitudinal data on quantitative immunoglobulin levels. (A) IgG. (B) IgA. (C) IgM. In all the panels, each line and symbol represent a single patient. The gray bold lines represent the 5th and 95th percentile levels of the age-matched reference values based on in-house unpublished data. Black line indicates trend. The black bold line in the panel C represents the 30 mg/dL limit used to define the severe IgM deficiency.