A high lymphocyte count indicates an increase in lymphocytes, which are white blood cells. Because lymphocytes aid in the battle against disease, it is natural to notice a brief increase following an infection.
In adults, a lymphocyte count significantly greater than 3,000 in a microliter of blood is considered lymphocytosis. The lymphocytosis threshold in children changes with age. It is high to have as many as 9,000 lymphocytes per microliter. The precise lymphocytosis criteria vary significantly between laboratories.
Types of Lymphocytes
Lymphocytes are classified into two types: B lymphocytes and T lymphocytes. These are referred to as B cells and T cells, respectively. Both types are derived from bone marrow stem cells. Some cells then go to the thymus, where they differentiate into T cells. Others are retained in the bone marrow and differentiate into B cells.
B cells are responsible for producing antibodies, which are proteins produced by the immune system in response to foreign substances called antigens. Each B cell is programmed to produce a single type of antibody. Each antibody binds to an antigen similarly to how a key binds to a lock, and when this occurs, the antigen is designated for destruction.
T cells are responsible for assisting the body in eliminating cancer cells and regulating the immune response to foreign chemicals. They accomplish this by eliminating cells in the body that have been infected with viruses or have become cancer.
The third type of lymphocyte, the natural killer or NK cell, originates in the same location as B and T cells. NK cells are rapidly activated in response to a variety of foreign chemicals and are highly specialized in the destruction of cancer cells and virus-infected cells.
B lymphocytes and T lymphocytes work together to fight infection.
Causes of High Lymphocyte Count
The following conditions result in an increase in lymphocyte count:
- Infection (bacterial, viral, other)
- Cancer of the blood or lymphatic system
- An autoimmune disorder causing ongoing (chronic) inflammation
Some specific causes include:
- Whooping cough
- Cytomegalovirus (CMV) infection
- Acute lymphocytic leukemia
- Hypothyroidism (underactive thyroid)
- Hepatitis A
- Hepatitis C
- Chronic lymphocytic leukemia
- Hepatitis B
- Other viral infections
Diagnosis of High Lymphocyte Count
Your doctor will do a blood test called a complete blood count (CBC) with differential to detect lymphocytosis. This test demonstrates an increase in white blood cells, with an abnormally high number of lymphocytes. Your doctor may prescribe additional diagnostic blood tests, such as flow cytometry, to determine the clonality of the cells (which is seen in a disorder called chronic lymphocytic leukemia).
A bone marrow biopsy may be performed to ascertain the etiology of lymphocytosis. Your medical history, present symptoms, medication list, and physical exam all assist doctors to discover the underlying cause of lymphocytosis.
Treatment of High Lymphocyte Count
Lymphocytosis is treated by addressing the underlying cause. It typically resolves as the underlying condition improves.