Lymphocyte countAbsolute lymphocytes
The white cells behind targeted immunity and immune memory.
Lymphocytes are the white cells responsible for specific, learned immunity: B cells make antibodies, T cells kill infected cells and coordinate the response, and natural killer cells patrol for abnormal ones.
It matters because they behave differently from neutrophils. Lymphocytes typically rise with viral infections rather than bacterial ones, and the balance between the two cell types is often more informative than either count alone.
In practice the count falls with physical stress, acute illness and steroid medication, and drifts down gradually with age. It is read alongside the neutrophil count and the total white cell count.