Lymphocyte percentageLymphocyte %

Lymphocytes are the white blood cells at the heart of the immune system's memory and targeted defence — the T cells and B cells behind long-term immunity. The lymphocyte percentage is the proportion of your total white cells that are lymphocytes.

It matters because the balance between lymphocytes and the other white cells shifts with infection, stress and age, and a relatively lower lymphocyte percentage has emerged as a marker used in biological-age estimates.

In practice, the percentage is read alongside the total white cell count and the rest of the differential; like most single blood markers it is best interpreted in context and over time rather than from one reading.