Lymphocytes in a blood test: normal range and results (LYM)
The percentage of all white cells (in the white cell differential). The absolute count (×10⁹/l) depends on the total white cell count and on the method the laboratory uses — for the exact interval see your own report.
- Updated
- 2026-09-30
- Every number with its source
What lymphocytes are
Lymphocytes are a group of white blood cells (leukocytes) that form the core of the immune system. They are made in the bone marrow and mature either there (B lymphocytes) or in the thymus gland (T lymphocytes). Lymphocytes recognise and destroy virus-infected cells, produce antibodies and “remember” past infections, so that the body reacts faster when it meets the same pathogen again. The amount of lymphocytes in the blood is determined as part of a full blood count with a white cell differential — it shows what percentage of all white cells are lymphocytes. This value is often assessed together with the total white cell count and the other types of white cell (neutrophils, monocytes, eosinophils, basophils), because an isolated change in the percentage may reflect not a change in the number of lymphocytes themselves but a change in another type of white cell. Changes in lymphocytes can be linked to viral infections, chronic bacterial infections, disorders of the immune system or cancers of the blood and lymphatic system (oncohaematological diseases).
The reference range for lymphocytes
| Group | Range, % | Source |
|---|---|---|
| Adults The percentage of all white cells (in the white cell differential). The absolute count (×10⁹/l) depends on the total white cell count and on the method the laboratory uses — for the exact interval see your own report. | 20–40 | MedlinePlus Reviewed 2025-02-03 |
When lymphocytes are tested
- As part of a full blood count with a white cell differential — during a preventive check-up or an assessment of general health
- When an infection is suspected — with a fever, a sore throat, enlarged lymph nodes or prolonged tiredness
- To monitor a known viral infection (for example infectious mononucleosis) or how it is progressing
- To assess the state of the immune system, for example before or after chemotherapy or radiotherapy
- When a disease of the blood or lymphatic system (leukaemia, lymphoma) is suspected on the basis of other symptoms or test results
- To monitor a chronic condition that can affect the immune system (for example HIV infection, an autoimmune disease)
How to prepare
- Special preparation is usually not needed — you do not have to fast before the test
- It is worth telling your doctor about all the medicines you take, since some of them can affect the white cell and lymphocyte count
A raised lymphocyte count (lymphocytosis)
A raised lymphocyte count (lymphocytosis) can show that the body is fighting a viral infection. According to MedlinePlus, possible causes are a chronic bacterial infection, viral illnesses (mumps, measles), infectious mononucleosis, tuberculosis, hepatitis, and also lymphocytic leukaemia. Other blood values and the clinical picture help tell the cause apart.
- A viral infection (for example infectious mononucleosis, mumps, measles)
- Whooping cough or rubella
- A chronic bacterial infection
- Tuberculosis
- Hepatitis
- Lymphocytic leukaemia or another lymphoproliferative disease
What is usually assessed alongside a raised result:
- Whether there are signs of an infection — a fever, a sore throat, enlarged lymph nodes
- The total white cell count and the ratio of the other types of white cell (neutrophils, monocytes)
- Whether it is worth repeating the test after some time, so that the change over time can be seen
- With a long-lasting or large increase and no clear infection — further investigation of the blood and lymphatic system
A reduced lymphocyte count (lymphopenia)
A reduced lymphocyte count (lymphopenia) can, according to MedlinePlus, be linked to chemotherapy, radiotherapy, HIV/AIDS, leukaemia, sepsis, the use of steroid medicines or ageing. It is always worth assessing what the value means together with a full blood count and the clinical condition.
- Chemotherapy or radiotherapy
- HIV/AIDS
- Leukaemia
- Lymphatic cancer (lymphoma)
- Sepsis (a severe infection with a whole-body response)
- The use of steroid medicines
- Ageing
What is usually assessed alongside a reduced result:
- A full blood count and an assessment of the other types of white cell
- A review with your doctor of the medicines you take, especially those that suppress the immune system
- An assessment of signs of an infection or of a chronic condition
- Repeating the test to follow the change over time
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Frequently asked questions
›What is the normal lymphocyte count in blood?
According to the MedlinePlus blood differential test, lymphocytes in adults make up 20–40% of all white blood cells (leukocytes). The absolute count (×10⁹/l) depends on the total white cell count — you will find your laboratory's exact interval on your own report.
›What is lymphocytosis?
Lymphocytosis is a raised number of lymphocytes in the blood, above the limit of the reference range. It can be linked to a viral infection (for example infectious mononucleosis), a chronic bacterial infection, tuberculosis, and also to a lymphoproliferative disease.
›What is lymphopenia?
Lymphopenia is a reduced number of lymphocytes in the blood. According to MedlinePlus, it can be linked to chemotherapy, radiotherapy, HIV infection, leukaemia, a severe infection (sepsis) or the use of steroid medicines.
›Does a raised lymphocyte count always mean a serious illness?
No. Raised lymphocytes can also be linked to a viral infection (for example mumps, measles or infectious mononucleosis). A small and temporary deviation from the range is not always significant — the result should be discussed with a doctor together with the other blood values and any symptoms.
›How do lymphocytes differ from leukocytes?
Leukocytes (white blood cells) are the general group of cells that make up the immune system, while lymphocytes are one part of that group, making up about 20–40% of all leukocytes. The other types of leukocyte are neutrophils, monocytes, eosinophils and basophils.
›Do I need any special preparation for a lymphocyte test?
No — according to MedlinePlus no special preparation is needed and you do not have to fast before the test. It is worth telling your doctor about the medicines you take, since some of them can affect the result.
›What is the normal absolute lymphocyte count?
The patient handbook on sundhed.dk, Denmark's national health portal, gives a reference interval for lymphocytes in adults of 1.30–3.50 ×10⁹/l (billion/l). The percentage (20–40 %) and the absolute count are assessed together, and your own laboratory's exact interval is printed on your result sheet.
Sources
Related markers
This site is not an emergency service. If severe chest or head pain, breathlessness, confusion, difficulty speaking, heavy bleeding or another acute problem has come on suddenly — do not wait for tests, call 112.
This information is not a diagnosis and does not replace a consultation with a doctor. Reference ranges depend on the laboratory, your age and sex — always compare your result with the range printed on your own report.