Q. What are the effects of a low total leukocyte count (TLC) count?
White blood cells (leukocytes) comprise granulocytes (cells with granules in their cytoplasm) and mononuclear cells. Granulocytes are of three types – neutrophils, eosinophils and basophils while mononuclear cells are lymphocytes and monocytes. The normal total leukocyte count (TLC) varies with the age of a person. It also has a diurnal cycle i.e. counts vary during a 24 hour day. Normally they range from 4000 to 10,000 per ml in an adult. Leukopaenia is a decrease below the accepted normal range of total leukocytes. This reduction may be due to a decrease in granulocytes, lymphocytes or monocytes and is respectively called absolute neutropaenia, absolute lymphopaenia and absolute monocytopaenia. The causes for each of these are many. Usually only one type of cell is responsible for this decrease, but there may be a simultaneous decrease in several cell types and this can be judged by a differential leukocyte count. The range of each of these cells also varies with the age of an individual. There are numerous causes for decrease in neutrophils, lymphocytes etc. Neutropaenia when accompanied by lymphocytopaenia (or monocytopaenia) is a more serious problem than neutropaenia alone.
Neutropaenia leads to an increased susceptibility to bacterial and fungal infections while lymphocytopaenia predisposes to recurrent viral, fungal, or parasitic infections. Neutropaenia may be classified as mild (1000 to 1500/µl), moderate (500 to 1000/µl), or severe (< 500/µl). Acute neutropaenia occurs over a few days and is often due to rapid neutrophil consumption accompanied by impaired production. This can be life threatening, especially in immunocompromised patients. Chronic neutropaenia (lasting for months or years) is usually caused by decreased neutrophil production or excessive sequestration of neutrophils in the spleen. The commonest cause of neutropaenia is drugs while it may be caused transiently by some viral infections and sepsis. It may also be due to megaloblastic anaemia caused by vitamin B12 or folate deficiency.
Lymphocytopaenia is defined by a total lymphocyte count of < 1000/µl in adults or 1500/µl at 2-6 years or < 3000/µl in children under 2 years of age. The condition may be inherited lymphocytopaenia when associated with inherited immunodeficiency diseases or acquired. AIDS is the most common infectious disease associated with lymphocytopaenia while it can be secondary to autoimmune disorders, drugs, etc.