@article{0dae6fbd29864ebb86e64627d5e289ff,
title = "Pre-analytical and biological variability in circulating interleukin 6 in healthy subjects and patients with rheumatoid arthritis",
abstract = "Interleukin (IL)-6, a key player in the inflammatory response, may be a useful biomarker in rheumatoid arthritis (RA). The aim was to determine analytical variability, a reference interval in healthy subjects, and long- and short-term variation in serum and plasma IL-6 in healthy subjects and RA patients. An enzyme-linked immunosorbent assay from R&D was used for determination of serum and plasma IL-6. The IL-6 concentration did not depend on the type of anticoagulant used or the 3-h time delay between sampling and processing or repeated freeze-thaw cycles. The median plasma and serum IL-6 in 318 healthy subjects were 1.3 pg ml(-1) (range 0.33-26) and 1.4 pg ml(-1) (range 0.25-23), respectively. The median coefficient of variation in plasma IL-6 in 27 healthy subjects during 1 month, and repeated after 6 and 12 months were 27%, 31% and 26%, respectively. No significant long-term changes were observed in serum IL-6 over a 3-year period (14%, p = 0.33). Exercise (cycling) increased serum IL-6 in healthy subjects but not in RA patients. In conclusion, circulating IL-6 is stable regarding sample handling and shows little variation over time. Changes in IL-6 concentrations > 60% (2 times the biological variation) are likely to reflect changes in disease activity and not only pre-analytical or normal biological variability.",
keywords = "Adolescent, Adult, Arthritis, Rheumatoid, Biological Markers, Blood Specimen Collection, Circadian Rhythm, Exercise, Female, Humans, Interleukin-6, Male, Middle Aged, Reference Values",
author = "Knudsen, {Lene S} and Christensen, {Ib J} and Tine Lottenburger and Svendsen, {Mads N} and Nielsen, {Hans J} and Lone Nielsen and Kim H{\o}rslev-Petersen and Jensen, {Jens E B} and Gina Kollerup and Johansen, {Julia S}",
year = "2008",
doi = "10.1080/13547500701615017",
language = "English",
volume = "13",
pages = "59--78",
journal = "Biomarkers",
issn = "1354-750X",
publisher = "Taylor and Francis Ltd.",
number = "1",
}