Lymphocytes

Norm

Adults
absolute numbers 1.0–4.5× 10⁹/l
percentages 20–45%
Children (absolute numbers)
up to 1 week 3.9–7.5× 10⁹/l
2 weeks – 3 years 3.8–9.5× 10⁹/l
4–13 years 1.5–8.0× 10⁹/l
Children (percentages)
up to 1 week 25–35%
2 weeks – 3 years 45–75%
4–13 years – 35–55%

Blood EDTA

Purple cap, smear

Lymphocytes – a highly heterogeneous population of blood cells. However, when examining a smear under a microscope, lymphocytes appear to be relatively uniform cells.

Absolute lymphocyte counts are important for diagnosis. If the test is not performed with a hematological analyzer, the absolute count can be calculated by multiplying the total white blood cell count by the percentage of lymphocytes (similar to the examples given above; see, for example, “Basophils”). A hematological analyzer usually provides lymphocyte values immediately in both percentage and absolute numbers. Relative percentage lymphocytosis is more commonly found, the cause of which is granulocytopenia (neutropenia). An increase in the percentage of lymphocytes, but with a total white blood cell count lower than 4×10⁹/l, can be considered as relative lymphocytosis. A marked lymphocytosis (more than 15×10⁹/l) can be caused by the following pathologies:

• infectious mononucleosis;
• acute infectious lymphocytosis;
• pertussis;
• chronic lymphocytic leukemia;
• acute lymphoblastic leukemia.

Other causes of lymphocytosis rarely result in such a significant increase in lymphocyte count. It is important to note that lymphocytosis of 15×10⁹/l does not necessarily indicate any of these pathologies. These diseases sometimes manifest with only a slight lymphocytosis.

Viral infection is the most common cause of lymphocytosis. In the case of a viral infection, lymphocytosis may sometimes be relative. This is because viral infections usually lead to a decrease in neutrophil count rather than an increase in lymphocyte count in peripheral blood. In viral infections, large granular lymphocytes may sometimes be found (see “Mononuclear cells”). It is generally believed that the combined count of atypical lymphocytes, mononuclear cells, and plasma cells in peripheral blood should not exceed 5–10%. If this count is higher, the likelihood of a viral infection is very high.

Conditions where an increase in atypical lymphocytes, plasma cells, and mononuclear cells is found:

• infectious mononucleosis;
• EBV (Epstein-Barr virus infection);
• CMV – cytomegalovirus infection;
• toxoplasmosis;
• hepatitis;
• AIDS;
• adenovirus infection;
• Herpes simplex infection;
• drug allergy.

An acute bacterial infection usually does not cause lymphocytosis. Pertussis is an exception. Pertussis usually affects non-immunized children. Lymphocytosis can reach 30×10⁹/l or more. Chronic specific infections such as tuberculosis, brucellosis, syphilis, typhoid conditions can also present with lymphocytosis. Infectious mononucleosis is characterized by fever, exudative tonsillitis, and lymphadenopathy. Another pathology related to lymphocytosis, infectious lymphocytosis, most commonly occurs in children or adolescents. The incubation period of infectious lymphocytosis is 2–3 weeks. Lymphadenopathy and splenomegaly are usually not found. It is believed that the etiological factor is a viral infection. The total lymphocyte count can increase to 100×10⁹/l or more. Eosinophilia is sometimes found.

Conditions where finding lymphocytosis necessitates a bone marrow examination:

• immature lymphocytes (lymphoblasts) found in peripheral blood smears;
• persistent lymphocytosis without clear signs of acute or subacute infection;
• normoblasts and/or young granulocytes found in the blood.

When suspecting malignant transformation of lymphocytic stem cells, it is useful to perform lymphocyte phenotyping (see “Flow cytometry”). By determining their phenotype, it is possible to know whether it is a monoclonal or polyclonal proliferation, assess prognosis, and treatment.

Lymphocytes are not only various cellular components of the immune response (cellular immunity depends more on T lymphocytes, humoral immunity on B lymphocytes), but also a group of various blood stem cells. All other blood cells can develop from these stem cells. They can be distinguished using immunological phenotyping based on CD markers. Morphologically, all stem and poorly differentiated hematopoietic cells resemble lymphocytes. Sometimes, in lymphomas, “abnormal” lymphocytes can be found, most commonly with indented nuclei. These can be T lymphocytes from lymph nodes or mycosis fungoides syndrome. Lymphomas rarely release cells into circulation, lymphogranulomatosis never progresses to leukemia. Viral infection often causes both lymphocytosis and lymphocytopenia. One of the most common causes of leukopenia can be severe viral infection. In chronic lymphocytic leukemia, bone marrow biopsies are examined, and an additional diagnostic feature is Gumprecht’s shadows. In chronic lymphocytic leukemia, the condition of other hematopoietic stem cells is important: as platelet count and hemoglobin concentration decrease, the prognosis worsens.

Source | Handbook of Basic Laboratory Tests | Doctor of Medical Sciences Gintaras Zaleskis