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Lymphocytosis - Causes, Symptoms, Diagnosis, and Treatment

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Lymphocytosis is an increase in the number of lymphocytes which are a type of white blood cells in case of infection. Read the article to know more.

Medically reviewed by

Dr. Abdul Aziz Khan

Published At May 11, 2023
Reviewed AtFebruary 27, 2024


Lymphocytosis usually occurs due to the body’s immune response against any external infectious agent. The number of white blood cells called lymphocytes increases in cases of infections or diseases. Lymphocytosis cannot be prevented but can be treated by eliminating the underlying pathology.

What Is Lymphocytosis?

A higher-than-normal count of lymphocytes (white blood cells) in the blood serum is known as lymphocytosis. They are a type of white blood cells that play a pivotal role in the host’s immune system thereby helping the host’s body fight any type of infection.

A temporary rise in the lymphocyte count in the blood usually suggests that the body is functioning properly to fight against the germ particles. Very rarely, lymphocytosis is seen as a sign of serious illness or disease.

Having greater than 4,000 lymphocyte cells in one microliter of blood is considered lymphocytosis in adults. Any individual can acquire this condition.

Who Is at High Risk of Developing Lymphocytosis?

Lymphocytosis is frequently seen in individuals who:

  • Recently had a viral infection.

  • Autoimmune systemic inflammatory disorders such as rheumatoid arthritis.

  • Had undergone severe illness such as trauma.

  • Had removal of the spleen.

  • Had blood cancer such as leukemias or lymphomas.

What Are the Causes of Lymphocytosis?

A high lymphocyte count in the blood suggests that the body is fighting against some infection or inflammatory disease. Cancer which is a serious illness can cause increased lymphocyte levels in the blood. Lymphocytosis can be caused by many medical conditions:


Malignant Cancers:

Lymphocytosis is usually presented as an initial clinical sign in certain blood cancers such as leukemia or lymphoma (cancer of the lymphatic system). Certain cancers associated with lymphocytosis include:

Other predisposing factors include:

  • Chronic cigarette smoking.

  • Allergy to certain medicines.

  • Stress in response to a medical emergency.

  • Some autoimmune diseases.

  • Removal of the spleen.

What Are the Clinical Symptoms of Lymphocytosis?

As such, lymphocytosis is not responsible for causing any signs and symptoms. However, one may experience the symptoms of the underlying systemic disease that is causing an increase in the lymphocyte count also. Therefore, the symptoms may vary from low to severe depending on the pathologic cause. Usually, a high lymphocyte count is discovered while taking a laboratory blood test.

How to Diagnose Lymphocytosis?

The healthcare provider will depend on the medical history, existing signs and symptoms, current usage of pharmacological drugs, and a thorough physical examination to determine the cause of lymphocytosis. The doctor may also suggest a blood test to check the lymphocyte count in the blood. The healthcare provider may ask certain questions about the current lifestyle and any habit to rule out the risk for sexually transmitted diseases, etc.

In case the lymphocyte count is high, the doctor may advise the patient to again take a blood test to see if the rise in lymphocyte count is temporary. If the lymphocyte count remains high then the doctor may suggest a few additional tests to identify the underlying cause. He may even refer the patient to a hematologist (blood specialist) for the correct diagnosis.

The healthcare provider may suggest the following tests:

  • Complete Blood Count- Complete blood profile with differential leukocyte count will help to exhibit a higher-than-normal lymphocyte count.

  • Flow Cytometry Test- This test is done to evaluate if there is any clonal expansion of lymphocytes such as seen in chronic lymphocytic leukemia, a type of blood cancer.

  • Bone Marrow Biopsy- The biopsy of the bone marrow will help to identify the main cause of lymphocytosis.

What Is the Treatment of Lymphocytosis?

The treatment of lymphocytosis involves the resolution of the existing underlying pathology causing an increased lymphocyte count.

If the body is producing lymphocytes to fight the infection, it is not necessary to require treatment. The body’s immune system is sufficient to take care of infectious diseases. However, if the spike in lymphocyte count is because of malignant cancer, the healthcare provider will advise the patient on the treatment options related to the tumor.

The patient should contact his healthcare provider if the infection is persistent or the symptoms worsen with time. The doctor will then suggest additional tests to determine the exact pathologic cause. The lymphocyte count will come to normal levels once the patient starts receiving treatment for the existing underlying pathology.

What Precautions are Needed to Prevent Lymphocytosis?

Lymphocytosis cannot be prevented. However, one can reduce the chance of acquiring the infection by following these simple steps:

  • Do not come in physical contact with a person suffering from a contagious disease.

  • Do not share the personal items with any diseased person.

  • Hands should be washed frequently using Dettol and water.

  • Disinfect all the surfaces that have a risk of carrying germs.

What Is the Prognosis After Treatment of Lymphocytosis?

The lymphocyte levels usually come to normal once the treatment is completed for the underlying pathology.


Lymphocytosis can be seen in infectious diseases or even in certain types of cancers like leukemia or lymphoma. The lymphocyte count increases in case of lymphocytosis. The lymphocyte levels return to normal once the body clears the infection. If the lymphocyte count does not return to normal, the patient should immediately consult a doctor. The doctor may suggest a few additional tests to identify the exact cause of lymphocytosis.

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Dr. Abdul Aziz Khan
Dr. Abdul Aziz Khan

Medical oncology


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