Establishing Reference Intervals for Adult Lymphocyte Subsets: Single-Platform Volume Analysis Reveals Age- and Sex-Specific Trajectories of Immunosenescence.

BACKGROUND: Current clinical reference intervals for lymphocyte subsets lack age- and sex-specific stratification, limiting accurate immune assessment. This study aimed to establish such stratified reference intervals in a large cohort of healthy adults aged 20-60 years. METHODS: A total of 1760 healthy adults were included. The absolute counts and percentage distributions of peripheral blood (PB) lymphocyte subsets were determined via flow cytometry (FCM) using a single-platform volume method. Differences between age groups and sexes were then compared. RESULTS: The absolute counts of total T cells and CD8+ T cells decreased with advancing age, whereas the absolute counts of CD4+ T cells remained relatively stable, although their percentage increased with age. There was a significant difference in immunological age between the 20-40-year-old and 41-60-year-old groups. Concurrently, the results of this study revealed immunological sexual dimorphism; however, this disparity tended to diminish in the 51-60-year-old group because of changes in female sex hormones. CONCLUSION: This study established refined reference intervals for adult lymphocyte subsets. The physiological ageing of the immune system constitutes a nonlinear dynamic process, and the establishment of two-dimensional reference intervals based on both sex and age is recommended.