Lymphocytopenia By David C Dale, MD, University of Washington Reviewed / Revised Apr 2023 View Patient Education Etiology Symptoms and Signs Diagnosis Treatment Key Points Topic Resources Absolute Lymphocyte Count Causes of Lymphocytopenia Lymphocytopenia is a total lymphocyte count of < 1000 / mcL (1 × 10 9 / L) in adults or < 3000 / mcL (< 3 × 10 9 / L) in children < 2 years.