CD4 and immunodeficiency disease: Eighteen percent (25) of 137 children age 1 to 3 years had CD4+ T-lymphocyte percentages ≤30%, the threshold for immunodeficiency in this age group, with 16 meeting the criterion for mild (CD4+ 25% to 30%), 6 for advanced (CD4+ 20% to 24%), and 3 for severe (CD4+ < 20%) immunodeficiency.