@article{e5efb5b0dbc311dc860c000ea68e967b,
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.",
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 = "2007",
month = sep,
day = "3",
doi = "10.1080/13547500701615017",
language = "English",
volume = "13",
pages = "1--20",
journal = "Biomarkers",
issn = "1354-750X",
publisher = "Informa Healthcare",
number = "1",
}