Encyclopedia / L / Lymphocyte Counts

Lymphocyte Counts


Lymphocytes (monomorphonuclear lymphocytes) are cells present in the blood and lymphatic tissue. Lymphocytes are derived from the stem cells from which all blood cells arise. They are the main means of providing the body with immune capability.


The lymph channels (lymphatics) are an extensive system of branching vessels that carry the lymphatic fluid formed in the tissues back to the bloodstream. Along the channels of the larger lymph vessels are clusters of lymph nodes. There are hundreds of lymph nodes in the body.

Lymph nodes are normally small, soft and flat. The majority of nodes in most healthy people cannot be felt, though in some healthy individuals, especially children, small nodes in the neck, armpit, or groin may be palpable (felt).

The lymph nodes help fight disease by filtering invading organisms out of the lymph fluid and by producing cells and antibodies that attack them. Thus, in the presence of certain infections and some other diseases, the lymph nodes may enlarge as part of the body's defense reaction.

It is believed that lymphocytes are responsible for the storage of immunologic memory. This means that a second contact with an antigen elicits an accelerated and increased response.

The normal values of lymphocytes are 20 to 40 percent of total leukocyte count (relative value) or 10,000-4,000/mm3.

Clinical Implications

Lymphocytosis (a potentially abnormal increase in the amount of circulating lymphocytes) is measured with the following values:

  • Above 9000/mm3 in infants and young children ages 4 years and younger
  • Above 7000/mm3 in children ages 5 through 12 years
  • Above 4000/mm3 in people 13 years and older

Conditions causing or associated with lymphocytosis:

  • Infectious lymphocytosis - occurs mainly in children (95 percent of lymphocytes in this condition are small, mature lymphocytes)
  • Infectious mononucleosis - caused by Epstein-Barr virus, most common in adolescents and young adults, characterized by atypical lymphocytes
  • Cytomegalovirus infection and other viral infections
  • Most viral upper respiratory infections, atypical pneumonia
  • Other viral diseases such as mumps, rubella, rubeola
  • Infectious hepatitis
  • Some bacterial infections such as tuberculosis and syphilis
  • Acute and chronic lymphocytic leukemia, lymphoma
  • Toxoplasmosis
  • Graves' disease
  • Lymphopenia (a decrease in the amount of circulating lymphocytes) occurs:
  • In Hodgkin's disease
  • In lupus erythematosus
  • After administration of ACTH and cortisone
  • After burns or trauma
  • In chronic uremia
  • In Cushing's syndrome
  • In early acute radiation syndrome
  • Many congential immunodeficiency states
  • AIDS
  • Aplastic anemia
  • Tuberculosis


Can lymphocytes increase or decrease slightly and still be normal?

Are there any other defects that may cause an increase or decrease in lymphocytes?

Can medications alter a lymphocyte count?