Lymphopenia is the condition in which there exists an abnormally low number of lymphocytes in the blood.
Lymphopenia can be caused by various types of chemotherapy, such as with cytotoxic agents or immunosuppresive drugs. Some malignancies in the bone marrow will also cause lymphopenia.
A decreased number of lymphocytes (notably T cells) is present in those with AIDS. People exposed to large doses of radiation, such as those involved with Chernobyl can also exhibit a lymphopenia.
Lymphopenia may be present as part of a pancytopenia , when all the blood cells are of decreased number. This can occur in marrow failure .