High and low lymphocytes: what they are and what they tell you

Lymphocytes are the white blood cells that carry immune memory: they recognise viruses and bacteria you have met before. Your report usually shows them twice, as a percentage and as an absolute count. When they are out of range, a viral infection, current or just over, is often behind it.

Why we test them

Lymphocytes are one of the five types of white blood cell in a full blood count, in the part called the differential. Some make antibodies, others recognise and destroy cells infected by a virus.

They live a long time and they remember. That is why, after an infection or a vaccine, your body responds faster the next time.

A result out of range is usually the sign of a recent infection. It matters more if it stays low over time. In a large study of older adults, a low absolute count was linked to more health problems in the years that followed.

What they tell you, and what they do not

If they are high, your body is usually fighting a virus or has just finished doing so. Glandular fever (mononucleosis) is the typical case.

If they are low, a current infection, cortisone or a very long effort are often behind it. They usually return to normal once the cause passes.

And the percentage alone can mislead. If your neutrophils drop, the lymphocyte percentage rises even when their number stays the same. That is why the absolute count matters.

That is why they are read together with other tests:

Normal lymphocyte levels

Your report usually lists lymphocytes twice. The percentage says what share of your white cells are lymphocytes. The absolute count says how many there are in a microlitre of blood. If there is only the percentage, the absolute count is the percentage times your white cell count, divided by a hundred.

The lab decides what is normal, and prints its limits next to each line. They vary a little from lab to lab, and they are higher in young children than in adults.

The absolute count is written as x10⁹/L or x10³/µL: it is the same number. Some reports give it per mm³, multiplied by a thousand. It matters more than the percentage, because it does not shift when the other white cells change.

In the Rosa report you see your lymphocytes next to the rest of your blood count. Rosa also calculates the absolute count, from your total white cells.

If your lymphocytes are high or low

What causes high lymphocytes

This is called lymphocytosis, and it is usually temporary. Check the absolute count first: if it is normal, a high percentage usually comes from slightly lower neutrophils.

Symptoms of high or low lymphocytes

High or low lymphocytes cause no symptoms on their own. If there are any, they come from the cause.

A viral infection can bring fever, a sore throat, swollen glands and tiredness. With glandular fever, the tiredness can last for weeks.

Swollen glands for more than a few weeks, night sweats or weight loss without a reason should be seen by a doctor.

Low lymphocytes: what it means

This is called lymphopenia. A single low result is common and often temporary. A current viral infection, a few days of cortisone or severe physical stress, like an operation, are enough to lower them.

A very long effort also lowers them for a few hours. After a race, lymphocytes move from the blood into the tissues, and then come back.

It matters more if the absolute count stays low on two tests a few weeks apart. Then your doctor looks for the cause: some medicines, too poor a diet, more rarely a long-lasting infection or a disease of the immune system.

What to do if they are out of range

Usually nothing urgent. Where to start:

What can skew the result

A few things change the number for a while. It helps to know them before you read it.

When to worry

Talk to your doctor if:

With Rosa, lymphocytes of 5 x10⁹/L or more (absolute count) are always flagged to a doctor, who usually has the test repeated.

Frequently asked questions

What are lymphocytes? White blood cells that recognise viruses and bacteria and remember them. Some make antibodies, others destroy infected cells.

What are normal lymphocyte levels? The lab decides, and your report prints its limits for the percentage and the absolute count. Look mainly at the absolute count: just outside the limits, it is usually temporary. At 5 x10⁹/L or more, talk to your doctor.

High or low lymphocytes: when should I worry? Usually you do not need to: a virus can raise or lower them, and they settle on their own. Talk to your doctor if the absolute count is 5 x10⁹/L or more, or if they are still out of range on a second test. Do the same if you have swollen glands for weeks, night sweats, weight loss without trying or you get ill often.

High lymphocytes and low neutrophils: what does it mean? Often it is the same thing seen from two sides: when neutrophils drop, the lymphocyte percentage rises, for example after a virus. Many people of African descent, and some of Middle Eastern descent, naturally have lower neutrophils, with no higher risk of infection. If you have a fever, see a doctor the same day, and with neutrophils below 0.5 x10⁹/L call 112 or go to the emergency department.

Can high lymphocytes mean leukaemia? Rarely: the most common cause is an infection. If they stay high for months without a reason as you get older, your doctor can ask for flow cytometry to clarify it.

How often should they be checked? They are part of the blood count: Rosa measures them twice a year. If they are out of range, your doctor decides whether and when to repeat them.

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