Lymphocytes

Some laboratories use 1.0 to 4.5 or 1.5 to 4.0; children have much higher counts; use the range your lab printed.

Lymphocytes are the white blood cells that deal with viruses and that make antibodies and immune memory. They include B cells, T cells and natural killer cells, though the full blood count counts them all together. This is the absolute number in a given volume of blood.

It is part of the full blood count differential. Doctors look at it during viral illnesses, when the immune system may be weakened, with medicines that lower it, and when looking into blood conditions in which lymphocytes multiply.

• Viral infections, including glandular fever
• Some bacterial infections such as whooping cough
• Smoking
• Stress and strenuous exercise, briefly
• Some blood conditions, particularly in older adults
• Recovery after a bone marrow suppressing illness or medicine

• Viral infections including flu, COVID-19 and HIV
• Steroid medicines and other immune-suppressing medicines
• Chemotherapy and radiotherapy
• Stress, surgery and severe illness
• Autoimmune conditions
• Older age, slightly

• Exercise shortly before the test raises it for an hour or two
• Steroid tablets lower it as an expected effect
• A dip during a viral illness recovers over a few weeks
• It sits a little lower in the general population in older age

No fasting needed. A count taken during an infection is best repeated once well. A single high count is often repeated some weeks later before any further tests.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.