CD4 and common variable immunodeficiency: Immunodiagnostic criteria for CVID in children include antibody deficiency interpreted regarding age-matched reference values, along with low switched memory B cell numbers, below 70% of age-related normal values, concurrently without evidence of profound T cell deficiency, low CD4 T helper cell counts, low relative numbers of CD4 T cells to the child’s age, and absent T cell proliferation [2].