title: Intra-individual variability over time in serum cytokine levels among participants in the prostate, lung, colorectal, and ovarian cancer screening Trial.
abstract: BACKGROUND
  Serum 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).
  
  
  METHODS
  Levels 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.
  
  
  RESULTS
  Among 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).
  
  
  CONCLUSIONS
  These results suggest that measurements of most of the cytokines evaluated in this study were highly reproducible over five-year periods.
authors.affiliation: Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, MD 20892-7240, United States. hofmannjn@mail.nih.gov
authors.forename: Jonathan N
authors.initials: JN
authors.lastname: Hofmann
authors.forename: Kai
authors.initials: K
authors.lastname: Yu
authors.forename: Rachel K
authors.initials: RK
authors.lastname: Bagni
authors.forename: Qing
authors.initials: Q
authors.lastname: Lan
authors.forename: Nathaniel
authors.initials: N
authors.lastname: Rothman
authors.forename: Mark P
authors.initials: MP
authors.lastname: Purdue
mesh_terms: D000368:Aged; D015179:Colorectal Neoplasms / Q000097:blood / Q000175:diagnosis*; D016207:Cytokines / Q000097:blood*; D005260:Female; D006801:Humans; D057230:Limit of Detection; D008175:Lung Neoplasms / Q000097:blood / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D010051:Ovarian Neoplasms / Q000097:blood / Q000175:diagnosis*; D011471:Prostatic Neoplasms / Q000097:blood / Q000175:diagnosis*
chemical_list: D016207:Cytokines