Short CommunicationIntra-individual variability over time in serum cytokine levels among participants in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial

BackgroundSerum measurements of cytokines, mediators of various B and T cell activities, are important markers of inflammation and immune dysregulation. We assessed the reproducibility of serum cytokine measurements over a five-year period among participants in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO).MethodsLevels of 13 cytokines [interleukin (IL) 1β, IL-2, IL-4, IL-5, IL-6, IL-7, IL-8, IL-10, IL-12p70, IL-13, interferon-gamma (IFNγ), granulocyte macrophage colony-stimulating factor (GM-CSF), and tumor necrosis factor-α (TNFα)] in stored sera from three collections (study baseline,+1 year, and + 5 years) among 28 randomly selected PLCO participants were measured using a high-sensitivity Luminex xMap-based multiplex panel. Within- and between-subject components of variance were estimated from random effects models and were used to calculate the coefficient of variation (CV) and intraclass correlation coefficient (ICC) for analytes with <30% of samples below the limit of detection (LOD). Spearman correlation coefficients between measurements of the same analyte over time and between analytes were also calculated.ResultsAmong the six cytokines with <30% of samples below the LOD, we observed excellent reproducibility for IL-6, IL-7, IL-13, and TNFα (ICC ⩾ 0.73), and fair to good reproducibility for IL-8 (ICC = 0.55) and IL-10 (ICC = 0.60). Spearman correlation coefficients comparing paired measurements of each cytokine at baseline and at +5 years were high (ρ ⩾ 0.74) with the exception of IL-10 (ρ = 0.44).ConclusionsThese results suggest that measurements of most of the cytokines evaluated in this study were highly reproducible over five-year periods.

► We evaluated variability in serum cytokine levels in samples collected up to 5 years apart. ► Levels of IL6, IL7, IL8, IL10, IL13, and TNFα were consistent over time (ICC ⩾ 0.55). ► A single measurement of these cytokines is a good surrogate for levels over a 5 year period.