# Lymphocyte count

The absolute lymphocyte count (ALC) is the total number of lymphocytes circulating in your blood. That includes your T cells, B cells, and NK cells. It comes from the differential on a complete blood count. In adults, the normal range is about 1.0 to 4.0 × 10⁹/L. Lymphopenia (an ALC below 1.0 × 10⁹/L) is a recognized sign of immune deficiency. It shows up in HIV infection, autoimmune diseases, lymphoma, after chemotherapy or radiotherapy, and in severe malnutrition. With age, the absolute count tends to fall, and the mix shifts. Naïve T cells drop, while memory and effector cells pile up, a pattern called immunosenescence. Population studies consistently link a lower lymphocyte count to higher all-cause death, more frailty, and greater infection risk. ALC is also part of several validated biological-aging indices. And strikingly, lymphopenia was a strong predictor of severe COVID-19, which underscores its broader role as a marker of your immune reserve.

## Sources

- Pera A, Campos C, López N, Hassouneh F, Alonso C, Tarazona R, Solana R. (2015). Immunosenescence: Implications for response to infection and vaccination in older people. Maturitas. https://doi.org/10.1016/j.maturitas.2015.05.004

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_Canonical: https://longevity-switzerland.com/en/glossary/lymphocyte-count · Part of Longevity Cities · Updated 2026-06-22_