Lymphocytes are blood cells that are part of the immune system. Their function is to circulate in the blood and tissues to provide immune protection against foreign agents entering the body.
If the number of lymphocytes in the blood increases, there are many of them, then they speak of lymphocytosis. Its causes may include common infections such as whooping cough and mononucleosis, or non-infectious diseases such as lymphoproliferative conditions such as chronic lymphocytic leukemia.
Norm of lymphocytes
What number of lymphocytes is considered normal?
When we receive a blood test that indicates the leukocyte formula of the blood, we are dealing with relative indicators. To accurately determine the number of lymphocytes in a volumetric unit of blood (in μl), you need to make a simple calculation:
Absolute number of lymphocytes (ACLymph) = (total number of leukocytes (TCL) x % Lymph content)/100 = number of cells/μl
In adults, lymphocytosis is defined as a cell count greater than >4,000/µL (this may also be expressed as: >4,000/mm3 or >4.0 x 10(9)/L).
In young children, the normal absolute lymphocyte count can reach 8,000/µL.
Lymphocytes found in the blood are made up of different groups of cells called T cells, B cells, and natural killer (NK) cells. These groups of cells have different functional responsibilities in ensuring the body’s normal immune defense.
When a hematologist first sees a patient’s blood test with an elevated level of lymphocytes, The first question that needs to be answered quickly is whether these changes are reactive, that is, the increase in lymphocytes is associated with the body’s reaction to external influences, or malignant.
- Reactive lymphocytosis means the reaction of the immune system to any disease or condition occurring in the body. This reaction should resolve within 1-2 months after the cessation of the action of the factor causing it. An example of reactive lymphocytosis would be lymphocytosis caused by an infectious disease (whooping cough, viral infection).
- Malignant lymphocytosis is a manifestation of an independent lymphoproliferative disease, such as acute or chronic leukemia.
As can be seen from the examples given, an increased number of lymphocytes in a blood test can be either a completely harmless manifestation of common diseases or a basis for establishing a serious diagnosis.
In some cases, especially in the early stages of the disease, even an experienced laboratory technician cannot distinguish between reactive and tumor lymphocytosis when conducting a simple blood test. Often, the distinction between these conditions requires additional complex tests, such as determination of lymphocyte subpopulations, determination of chromosomal abnormalities in the nuclei of lymphocytes, molecular genetic tests, and bone marrow examination.
REACTIVE LYMPHOCYTOSIS.A common cause of reactive lymphocytosis is acute and chronic viral infections, which are most common in childhood and young adults. Reactive lymphocytosis may be accompanied by enlarged lymph nodes, liver and/or spleen. The accompanying enlargement of internal organs is neither an argument “for” the presence of a dangerous tumor process, nor an argument “against” it. In any case, the situation should be assessed by an experienced specialist.
Often, the distinction between reactive and tumor lymphocytosis (increased number of lymphocytes) requires additional complex tests, such as determination of lymphocyte subpopulations, determination of chromosomal abnormalities in the nuclei of lymphocytes, molecular genetic tests, bone marrow examination
Often, lymphocytosis in the blood can be accompanied by enlargement of the lymph nodes, liver and/or spleen. This can be a manifestation of both reactive and tumor processes
MOST COMMON CAUSES OF LYMPHOCYTOSIS
| INFECTIONS | |
| Viral | Ebstein-Barr virus (infectious mononucleosis) Cytomegalovirus Mononucleosis-like syndrome (adenovirus type 12, herpes virus type 6) HIV-1 Human T-cell leukemia virus type 1 Measles, chickenpox, rubella, hepatitis, sudden exanthema Infectious lymphocytosis (Coxsackievirus B2, enteroviruses (polio, etc.) Pertussis |
| Bacterial | Sometimes: cat scratch disease, tuberculosis; syphilis, brucellosis |
| Protozoal infections | Toxoplasmosis |
| Parasitic infestations | |
| NON-INFECTIOUS CAUSES | |
| Hypersensitivity reactions | Drug-related reactions Serum sickness Injury |
| Stress lymphocytosis | After removal of the spleen Heavy smokers Lymphocytosis of giant granular lymphocytes |
| Autoimmune processes | Rheumatoid arthritis |
| Endocrine diseases | Hyperthyroidism |
| PRE-TUMOR AND TUMOR DISEASES | |
| Pre-tumor conditions | B-cell lymphoproliferative disorder Malignant thymoma |
| Tumor diseases | Chronic lymphocytic leukemia Acute lymphoblastic leukemia Malignant non-Hodgkin’s lymphoma |
What’s important to remember?
- If lymphocytosis is noted in a general blood test, especially when the test is repeated several times, this is a reason to consult a doctor.
- To make an accurate diagnosis, additional examinations may be necessary, such as determining the infectious pathogen, the state of the immune system, or bone marrow examination;
- If changes in the blood are accompanied by enlargement of the lymph nodes, liver and/or spleen, then the enlarged organs should be assessed by an experienced specialist, preferably a hematologist or oncologist;
- In addition to laboratory tests, a diagnostic search for lymphocytosis, depending on the specific situation, may require a chest x-ray, ultrasound examination of internal organs, computed tomography, and sometimes cytological and histological examination of the bone marrow.