Lymphopenia (lymphocytes < 2000 / mcL [2.0 X 10 9 / L] at birth, < 4500 / mcL [4.5 x 10 9 / L] at age 9 months, or < 1000 / mcL [1.0 X 10 9 / L] in older children or adults) suggests a T-cell disorder because 70% of circulating lymphocytes are T cells. Leukocytosis that persists between infections may occur in leukocyte adhesion deficiency.