title: Detectability and reproducibility of plasma levels of chemokines and soluble receptors.
abstract: BACKGROUND
  Multiplex assays are available to measure an array of circulating chemokines, soluble cytokine receptors and growth factors. However, there is limited information regarding whether these analytes are suitable for large-scale epidemiological studies to assess their relationships with chronic diseases, including cancer.
  
  
  METHODS
  We examined detectability, assay repeatability, and 3-year within-subject reproducibility of plasma levels of 25 chemokines and 11 soluble receptors of cytokines and growth factors selected from the Human Millipore Panels. Plasma samples were obtained from 36 men (average age 62 years) and 17 women (average age 32 years) who participated in two epidemiological studies. Inter-assay and within-subject reproducibility were assessed by intraclass correlation coefficients (ICC).
  
  
  RESULTS
  All analytes, except lymphotactin (47% detectability), were detectable in >90% of plasma samples. Inter-assay reproducibility for all analytes in 36 men tested three times on separate days were good to excellent (ICCs: 0.71-1.00). Within-subject reproducibility in 17 women sampled three times in three years were excellent (ICC ≥ 0.75) for five chemokines (eotaxin, fractalkine, 6Ckine, eotaxin 3, and SDF-1α+β) and three soluble receptors (sIL-1R2, sIL-4R and sVEGFR2); ICCs were fair to good (0.4 ≤ ICC < 0.75) for 15 chemokines and eight soluble receptors. However, five chemokines (GRO, IP-10, MIP-1β, BCA-1, and MIP-3α) had ICC < 0.4, suggesting biological variability.
  
  
  CONCLUSIONS
  Multiplex assays for plasma levels of selected chemokines and soluble receptors showed good to excellent assay detectability and repeatability. Most analytes also had good 3-year within-subject reproducibility, indicating that a single measurement of these analytes may be used to assess biomarker-disease associations.
authors.affiliation: Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, NY, USA.
authors.forename: Ilir
authors.initials: I
authors.lastname: Agalliu
authors.affiliation: Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, NY, USA.
authors.forename: Xiaonan
authors.initials: X
authors.lastname: Xue
authors.affiliation: Department of Medicine, University of Vermont, Colchester, VT, USA.
authors.forename: Mary
authors.initials: M
authors.lastname: Cushman
authors.affiliation: Department of Pathology, University of Vermont, Colchester, VT, USA.
authors.forename: Elaine
authors.initials: E
authors.lastname: Cornell
authors.affiliation: Cancer Prevention Institute of California, Freemont, CA, USA ; Stanford Cancer Institute, Palo Alto, CA, USA.
authors.forename: Ann W
authors.initials: AW
authors.lastname: Hsing
authors.affiliation: Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, NY, USA.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Kaplan
authors.affiliation: Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, NY, USA ; Department of Medicine, Albert Einstein College of Medicine, Bronx, NY, USA.
authors.forename: Kathryn
authors.initials: K
authors.lastname: Anastos
authors.affiliation: Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, NY, USA ; Current address: Merck & Co., Inc., Whitehouse Station, NJ, USA.
authors.forename: Swapnil
authors.initials: S
authors.lastname: Rajpathak
authors.affiliation: Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, NY, USA.
authors.forename: Gloria Y F
authors.initials: GY
authors.lastname: Ho
keywords: Biomarker; Chemokines; Limit of detection; Soluble receptors; Within-subject variability