Day-to-day variation in plasma interleukin-6 concentrations in older adults.

Interleukin-6 (IL-6) is a pro-inflammatory cytokine commonly used in studies as a means of assessing chronic inflammatory status. Despite the use of plasma IL-6 as a marker of chronic inflammation few studies exist that examine the variability of plasma IL-6 within and between individuals. The purpose of this study was to assess inter- and intra-variability of plasma IL-6 concentration in men and postmenopausal women.