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3 Lymphocytes. LYMPH

Lymphocytes — B, T and NK cells of adaptive immunity: percentage vs absolute count, causes of lymphocytosis and lymphopenia.

Lymphocytes are the white blood cells of specific (adaptive) immunity. B lymphocytes produce antibodies, T lymphocytes recognise and kill infected or abnormal cells and coordinate the immune response, and NK (natural killer) cells destroy virus-infected and tumour cells without prior sensitisation. In the blood test lymphocytes are reported as a percentage of all white cells and, more reliably, as an absolute count.

Complete blood countWhite cell differentialImmunity

Share of white cellsabout 20–40 %

Absolute count (adults)1.0–4.0 ×10⁹/L

Childrenhigher, up to 9 ×10⁹/L

Lymphopenia< 1.0 ×10⁹/L

Figure 1. Lymphocytes are the second largest group of white blood cells in adults. In young children they often outnumber neutrophils.

Percentage versus absolute count

The percentage depends on the other white cells. In bacterial infection, for example, neutrophils increase and the lymphocyte percentage falls, even though the number of lymphocytes is unchanged. The absolute count is calculated as lymphocytes (×10⁹/L) = WBC × lymphocytes (%) / 100, and it is the value used for clinical decisions. In adults it is usually 1.0–4.0 ×10⁹/L (some laboratories use up to 4.8). Children have higher counts.

High lymphocytes — lymphocytosis

Group	Causes
Reactive (most common)	Viral infections — infectious mononucleosis (EBV), cytomegalovirus, hepatitis, influenza; pertussis; toxoplasmosis; tuberculosis
Stress lymphocytosis	Short-lived increase after trauma, heart attack, seizures or intense exercise
Other	Smoking, after splenectomy, hyperthyroidism
Clonal	Chronic lymphocytic leukaemia (persistent B lymphocytes ≥ 5 ×10⁹/L), lymphomas, large granular lymphocyte leukaemia

Reactive lymphocytosis disappears after the infection resolves. A persistent increase in an adult, especially in an older person or with enlarged lymph nodes, enlarged spleen, night sweats or weight loss, should be investigated with a blood smear and, if necessary, flow cytometry.

Low lymphocytes — lymphopenia

Acute infections (including COVID-19 and influenza), sepsis, physical stress
Corticosteroids and other immunosuppressive drugs, chemotherapy, radiotherapy
HIV infection (loss of CD4 T cells), tuberculosis
Autoimmune diseases (systemic lupus erythematosus), malnutrition, heavy alcohol use
Inherited immunodeficiencies (rare, mainly in children)

Mild, transient lymphopenia is common during illness. Persistent or marked lymphopenia raises susceptibility to viral, fungal and opportunistic infections. In population studies it has been associated with higher mortality.

When to see a doctor

Discuss the result if lymphocytes remain abnormal on repeated tests, or if abnormal values come with enlarged lymph nodes, fever, night sweats, weight loss, frequent or unusual infections.

References

Blumenreich MS. The white blood cell and differential count. In: Walker HK, Hall WD, Hurst JW, eds. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd ed. Boston: Butterworths; 1990. Chapter 153. ncbi.nlm.nih.gov/books/NBK261
Riley LK, Rupert J. Evaluation of patients with leukocytosis. Am Fam Physician. 2015;92(11):1004–1011. PMID: 26760415
Chabot-Richards DS, George TI. Leukocytosis. Int J Lab Hematol. 2014;36(3):279–288. doi:10.1111/ijlh.12212

This article is for general information and does not replace a consultation with a doctor. Laboratory results must be interpreted by a physician together with symptoms and other tests.

Published on 25 April 2024

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