Benign Lymphocytic Disorders

Lymphocytes are a class of white blood cells (WBCs) comprised of mature T-cells, B-cells, and natural killer (NK) cells that are important in the maintenance of both adaptive and innate immune responses. The normal adult absolute lymphocyte count (ALC) for a healthy adult ranges from 1 × 109/L to 4.0 × 109/L. Lymphocytosis is present when the ALC exceeds 5 × 109/L, whereas an ALC of less than 1.0 × 109/L is termed lymphocytopenia. A normal lymphocyte count is variable for pediatric patients based on the child’s age and is usually higher among infants and very young children. An ALC of 6 × 109/L for children and that of 9 × 109/L for infants are considered absolute lymphocytosis, whereas an ALC less than 2 × 109/L is considered lymphocytopenia for children aged 6 and younger. Lymphocytosis can be broadly divided into reactive and malignant categories. Lymphocytopenia is often associated with congenital or acquired immunocompromised status or post-cytotoxic therapy.