Lymphopenia

Definition: This means you don't have enough lymphocytes, which are a subset of white blood cells. The word is a combination of lymphocyte, which is a type of infection-fighting white blood cell, and penia, a word ending that means "deficiency."

Lymphocytes are a subset of white blood cells that are one of three main types of blood cells. The overwhelming majority of these cells are the red blood cells (erythrocyte), which bind to oxygen. The second most common, but still relatively few compared to the erythrocytes are the thrombocytes (platelets) that clot the blood. The least common types are the white blood cells (leukocytes), which are essential to the body's immune system. These cells form in the bone marrow and then enter the blood circulation or travel to other parts of the body. Wherever they are, they work to attack or identify parasites, viruses or harmful bacteria.

Reduced production of blood cells can be caused by many conditions, but it's also a common side effect from medication. For example, treatment for chronic viral hepatitis, with peginterferon and ribavirin, sometimes causes suppression of the white blood cells (leukopenia) and sometimes specifically neutropenia (low neutrophils) or lymphopenia.