This article is from the Interpretation Of Lab Test Profiles, by Ed Uthman firstname.lastname@example.org with numerous contributions by others.
Lymphocytosis is seen in infectious mononucleosis, viral
hepatitis, cytomegalovirus infection, other viral infections,
pertussis, toxoplasmosis, brucellosis, TB, syphilis, lymphocytic
leukemias, and lead, carbon disulfide, tetrachloroethane, and
arsenical poisonings. A mature lymphocyte count >7,000/uL is an
individual over 50 years of age is highly suggestive of chronic
lymphocytic leukemia (CLL). Drugs increasing the lymphocyte
count include aminosalicyclic acid, griseofulvin, haloperidol,
levodopa, niacinamide, phenytoin, and mephenytoin.
Lymphopenia is characteristic of AIDS. It is also seen in
acute infections, Hodgkin's disease, systemic lupus, renal
failure, carcinomatosis, and with administration of
corticosteroids, lithium, mechlorethamine, methysergide, niacin,
and ionizing irradiation. Of all hematopoietic cells lymphocytes
are the most sensitive to whole-body irradiation, and their
count is the first to fall in radiation sickness.