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Immune defense

Lymphocytes

Also known as: Lymphocyte count, Absolute lymphocyte count (ALC), Lymphocyte percentage (as part of a differential)

A lymphocyte test measures the number of lymphocytes — specialized white blood cells — circulating in your blood. Lymphocytes are central to your immune system and include T cells, B cells, and natural killer (NK) cells, each with different immune functions. They help the body fight cancer, foreign viruses, infections, and abnormal cells.

The lymphocyte percentage represents the proportion of your total white blood cells that are lymphocytes, while the absolute lymphocyte count measures the total number of lymphocytes in your blood. The absolute count is calculated by multiplying the lymphocyte percentage by the total white blood cell count.

Lymphocyte count is rarely, if ever, a stand-alone test but is instead almost always reported as part of a CBC with differential, which breaks down all types of white blood cells. Abnormal lymphocyte levels can point to infection, immune deficiencies, bone marrow disorders, or blood cancers.

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Key takeaways

  • Sample required: Blood.

  • Tests for: The number or percentage of lymphocytes, a type of white blood cell critical for immune defense.

  • Healthy range: Typically 1,000–4,800 cells/µL (absolute count) or 20–40 percent of total white blood cells in adults.

What can a lymphocyte test tell you?

A lymphocyte test can provide valuable information about your immune health:

While results offer insight, interpretation depends on other blood values, symptoms, and medical history. That's why it’s important to work alongside a provider to interpret results as part of a broader picture.

What is being tested?

Lymphocytes are a subgroup of white blood cells involved in adaptive immunity, which is the body’s ability to prevent future disease by remembering invaders it has encountered before. Major types include:

  • T cells. Regulate immune responses and directly attack infected or cancerous cells.

  • B cells. Produce antibodies to neutralize pathogens.

  • Natural killer (NK) cells. Destroy virus-infected and abnormal cells without prior sensitization.

A normal immune system depends on balanced numbers of these lymphocyte subtypes. The standard CBC measures total lymphocytes; specialized tests (like flow cytometry) can identify specific subsets.

Where is the lymphocyte test typically included?

A lymphocyte count is included in a complete blood count (CBC) with differential, which measures:

Who should get a lymphocyte test?

Providers may look at a lymphocyte test if you have:

  • Infection symptoms. Fever, swollen lymph nodes, or fatigue.

  • Signs of immune suppression. Frequent or severe infections.

  • Blood disorders. Unexplained bruising, fatigue, or enlarged spleen.

  • Autoimmune disease. Suspected or known lupus, rheumatoid arthritis, or similar conditions.

  • Cancer monitoring. To evaluate or follow the treatment of leukemia or lymphoma.

How Labs by Hers works

  • 1

    Book your test

    Schedule a lab draw in the Hers app at one of more than 2,000 convenient locations.

  • 2

    Get your results

    Review your lab results to understand which areas of your health may need attention.

  • 3

    Spot early signals

    Identify potential health risks or system imbalances before they become more serious.

  • 4

    Get your action plan

    Receive expert guidance tailored to your health profile and test results.

  • 5

    Improve over time

    Track your progress through a mid-year panel and ongoing provider check-ins.

Not available in all 50 states. Eligibility and provider order required. Lab results alone are not intended to diagnose, treat, or cure any condition. A provider will reach out about critical results and plans include access to 24/7 provider messaging.

Images for illustrative purposes only.

Frequently asked questions

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What causes changes in lymphocyte levels?

Increased levels (lymphocytosis) can result from a number of factors, including viral infections (including mononucleosis, hepatitis, and CMV), chronic bacterial infections (including tuberculosis and pertussis), hematologic malignancies (CLL, ALL), autoimmune diseases, and stress responses (including trauma and seizures).

Causes of decreased levels (lymphocytopenia) also include viral infections (including HIV and influenza) and autoimmune diseases (including lupus and rheumatoid arthritis). Additionally, immunodeficiency disorders (HIV/AIDS and congenital conditions), bone marrow suppression (from chemotherapy or radiation), corticosteroid use, severe malnutrition or protein loss, hematologic cancers (including lymphoma and leukemia) can also result in decreased lymphocyte levels. Low levels of lymphocytes may also be inherited as a genetic condition.

Can this test be done at home?

Not directly. CBC testing requires lab equipment, though at-home blood draws can collect samples.

What is a normal lymphocyte range?

Typically 1,000–4,800 cells/µL (absolute count) or 20–40 percent of total white blood cells in adults.

How long do results take?

CBC results, including lymphocytes, are often available within 24 hours.

What is considered a dangerous lymphocyte count?

Very low counts (<500/µL) raise concern for severe immunosuppression and infection risk. Very high counts may warrant testing for leukemia.

Does a high lymphocyte count always mean cancer?

No. Viral infections are another common cause. Cancer is considered mainly if the counts are very high or persistent.

How often should I get tested?

There is no set schedule. Testing is repeated if you have ongoing symptoms, known conditions, or to monitor treatment.

Is a lymphocyte test covered by insurance?

Yes. A lymphocyte test as part of a CBC is usually covered by insurance when it’s ordered for a medical reason, such as evaluating signs of infection, investigating immune system disorders, or monitoring certain treatments or medications that affect white blood cells. Coverage can vary depending on your plan. Insurance is not required for lab testing through Hers. 

What tests are related to this biomarker?

• Complete blood count (CBC) with differential

• Flow cytometry (to evaluate lymphocyte subsets)

• HIV test (if lymphocytopenia suspected)

• Bone marrow biopsy (if malignancy suspected)

The information provided here is for informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always talk to a qualified healthcare provider about your specific health concerns.

Related biomarkers

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Basophils (absolute count)

Basophils are a type of white blood cell that help your body respond to allergens and fight certain parasites.

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Basophils (percentage)

Basophils typically make up less than 1% of your total white blood cells and help trigger allergic responses and fight certain parasites. A healthy percentage means your blood contains the expected proportion of basophils, which are important for normal immune function.

Learn more about Basophils (percentage)

Eosinophils (absolute count)

Eosinophils are a type of white blood cell that help to control allergy-related inflammation and protect against certain parasites. A healthy count means your blood contains the expected number of eosinophils, which are important for normal immune function.

Learn more about Eosinophils (absolute count)

Eosinophils (percentage)

Eosinophils normally make up about 1-4% of your total white blood cells and help your body fight parasites and control allergy-related inflammation. A healthy percentage means your blood contains the expected proportion of eosinophils, which are important for normal immune function.

Learn more about Eosinophils (percentage)

Monocytes (absolute count)

Monocytes are a type of white blood cell that help your body defend against bacteria and clean up damaged cells. A healthy count means your immune system is working efficiently to support your healing and protect against infection.

Learn more about Monocytes (absolute count)

Monocytes (percentage)

Monocytes typically make up about 2-8% of your total white blood cells. They act as your body’s clean-up crew to remove damaged cells and help fight bacterial infections. A healthy percentage means your blood contains the expected proportion of monocytes, which are important for normal immune function.

Learn more about Monocytes (percentage)

Neutrophils (absolute count)

Neutrophils are the most common type of white blood cell and act as your body’s first line of defense against bacterial infections. A healthy count means your immune system is well-prepared to respond quickly to infection when needed.

Learn more about Neutrophils (absolute count)

Neutrophils (percentage)

Neutrophils are the most common type of white blood cell, typically making up 50–70% of your total white blood cells. They act as your body’s first line of defense against bacterial infections. A healthy percentage means your blood contains the expected proportion of neutrophils, which are important for normal immune function.

Learn more about Neutrophils (percentage)

White Blood Cell Count

White blood cells are an essential part of your immune system, helping your body fight infections and support healing. A healthy count means your immune defenses are strong and ready to respond in case infection arises.

Learn more about White Blood Cell Count

Systemic Immune-Inflammation Index (SII)

The systemic immune-inflammation index (SII) combines three key blood markers, platelets, neutrophils, and lymphocytes, to reflect the balance between inflammation and your immune defenses. A healthy SII means your immune system is well-regulated, not under excess inflammatory strain, and ready to defend your body against infection effectively.

Learn more about Systemic Immune-Inflammation Index (SII)

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Reviewed by Darragh O'Carroll, MD

Published 12/04/2025