What Does It Mean When Your Lymphocyte Count Is High or Low?

A high or low lymphocyte count on a complete blood count (CBC) is often explained by something temporary, such as a recent viral infection, a medicine, or physical stress. Lymphocytes are the white blood cells that coordinate much of your immune defense. A single abnormal value does not diagnose a disease, but a persistent result, or one that comes with symptoms, deserves a closer look. This article covers common causes, less common ones, and when to get care.

What a lymphocyte count measures

Lymphocytes are a type of white blood cell. The main groups are B cells, T cells and natural killer (NK) cells. Together they help your body recognize and respond to viruses and other threats, and they hold "memory" of past infections.

Your lymphocyte number comes from the white cell differential, which is part of a CBC. MedlinePlus describes blood count tests as a way to check the cells in your blood, including white cells. The differential reports lymphocytes either as a percentage of your white cells or as an absolute count (the actual number per unit of blood). The absolute count is usually more informative, because a percentage can look high or low simply because another cell type, such as neutrophils, changed.

Reference ranges differ between laboratories and by age, so the range printed on your own report is the one that applies to you. Children normally have a higher proportion of lymphocytes than adults. Ask your clinician how your result compares for your age.

Why one number is only a starting point

Lymphocyte counts move up and down. Clinicians usually interpret a result alongside your symptoms, your medicines, your other CBC values and, often, a repeat test. A mildly abnormal result in someone who feels well is often repeated before further testing; your clinician decides the timing.

High lymphocyte count (lymphocytosis)

Common causes

Several factors can raise lymphocytes. Many are temporary:

• Viral infections. Mononucleosis, influenza, cytomegalovirus and many childhood viral illnesses can raise the count while the immune system responds.
• Some bacterial infections. Whooping cough (pertussis) and tuberculosis are examples that can be associated with higher lymphocytes.
• Recovery from illness. The count can stay raised for a while after an infection has settled.
• Physical stress. Intense exercise, surgery or a major medical event can shift white cell numbers.
• Medicine reactions. Some drugs can affect lymphocyte counts. Review your medicine list with your prescriber or pharmacist.

Less common causes

Blood cancers that involve lymphocytes are much less common than infection as a reason for a high count, and one high result alone does not establish them. MedlinePlus describes chronic lymphocytic leukemia (CLL) as a cancer that often develops slowly, and it can be found on a routine CBC in people with no symptoms. Acute lymphocytic leukemia is a different condition, described on MedlinePlus as acute lymphocytic leukemia, and it generally causes more rapid symptoms.

Another finding clinicians may see is monoclonal B-cell lymphocytosis (MBL), a small population of similar B cells in people who do not have leukemia. A published Ontario review in PubMed Central discusses how clinicians approach investigation of MBL and CLL, including the question of whether some people are over-investigated. Whether further testing is needed depends on the details, which is a conversation for your clinician.

How a persistent high count is evaluated

If the count stays high, clinicians commonly review the blood smear under a microscope and may order flow cytometry, a test that identifies the types of cells present. The Ontario review is one example of how a single health system applies this kind of workup. Clinicians may also ask about fever, night sweats, weight loss, and swollen glands, and examine your lymph nodes, spleen and liver. The exact workup varies with your age and situation.

Low lymphocyte count (lymphopenia)

Common and temporary causes

• Acute illness or stress. Severe infections, surgery, trauma and critical illness can lower the count, sometimes briefly.
• Corticosteroids and other medicines. Steroids, chemotherapy, radiation and immune-suppressing drugs can reduce lymphocytes, and clinicians sometimes follow the count to monitor these treatments.
• Malnutrition. Severe protein-calorie malnutrition can lower lymphocyte counts, and it is usually recognized from other findings as well.
• Autoimmune conditions. Some, such as lupus, can be associated with lower lymphocytes. Your clinician may weigh this against other findings, which is also relevant if you have been told about a positive ANA test.

Infections and inherited conditions

HIV attacks a type of T cell and can lower lymphocyte counts. MedlinePlus explains HIV, and a clinician can arrange testing if it is a concern. Some inherited immune conditions can also cause low lymphocytes, usually showing up as repeated or unusual infections beginning early in life.

How a low count is evaluated

A low count by itself does not tell you the cause. Clinicians usually repeat the CBC, review your medicines and recent illness, and order targeted tests, such as HIV testing, when your history suggests them.

What low lymphocytes can feel like

Many people with a mildly low count have no symptoms. When the count is lower for longer, people may notice infections that occur more often, last longer, or are unusual. Neutrophils, another type of white cell, are a major factor in infection risk during chemotherapy, so a low lymphocyte count alone is a different situation. Oncology teams commonly treat a temperature of 100.4°F (38°C) or higher as an emergency in people with low neutrophils. If you are receiving chemotherapy or have been told your neutrophil count is low, call your treating team's emergency line right away and go to the emergency room if they direct you to or if there is any delay reaching them. Do not take fever reducers before calling, because they can mask a fever; your treating team will tell you what to take, if anything.

How the count fits with the rest of the CBC

Lymphocytes are one line of the differential. If your total white cell count is high, the related articles below on high white blood cell count and low neutrophils explain those broader pictures and that separate cell type. Here the focus stays on lymphocytes specifically.

Clinicians often look for patterns. A high lymphocyte count with low red cells or platelets, for example, may lead them to look more closely at the bone marrow. A low lymphocyte count after starting a new medicine points the conversation toward that drug. Most routine differentials come from automated analyzers; a blood smear or flow cytometry may be added when the result is persistent or unexplained. Your report's own range governs how your result is read.

What you can do with an abnormal result

• Check whether you were sick, exercising hard, or recovering from illness around the time of the blood draw.
• Make a list of all prescription and over-the-counter medicines and supplements. Share it with your clinician, who can tell you whether any may be relevant.
• Write down symptoms, such as fevers, night sweats, unexplained weight loss, swollen glands, or frequent infections, and when they started.
• Bring prior CBC results if you have them. A trend over time often says more than one value.
• Tell your clinician about the result so they can decide whether a repeat test, a blood smear, or further testing is appropriate for you. Please do not start or stop any medicine on your own because of a lab value. Ask the prescriber first.

Children and older adults

Children have different normal ranges, and viral infections commonly raise their lymphocytes. A child's result should be read against a pediatric range by their pediatrician. Childhood leukemia is much less common than infection as an explanation, and MedlinePlus describes it in childhood leukemia. In older adults, slowly developing lymphocytosis is sometimes found on routine labs, and clinicians weigh it with the rest of the picture.

When to seek medical care for an abnormal lymphocyte count

Most abnormal lymphocyte counts are not emergencies. Fever of 100.4°F (38°C) or higher during chemotherapy or with a known low neutrophil count needs urgent contact with your oncology team, as described above. Call 911 for severe trouble breathing, new confusion, fainting that does not quickly resolve or comes with chest pain or a racing heartbeat, or bleeding that does not stop with firm pressure. The emergency box below lists the full set of features that need emergency care and those that need an appointment. For swollen glands, night sweats, unexplained weight loss or repeated infections, book an appointment with your clinician. These symptoms can accompany lymphoma or leukemia, and MedlinePlus describes Hodgkin lymphoma as one example. They have many more common causes, but they deserve evaluation.

When to Seek Medical Care