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Diurnal, Weekly, and Long-Time Variation in Serum Concentrations of YKL-40 in Healthy Subjects

¹ Department of Rheumatology, Herlev Hospital; Departments of ² Surgical Gastroenterology and ³ Endocrinology, Hvidovre Hospital; ⁴ Department of Rheumatology, Bispebjerg Hospital, University of Copenhagen; ⁵ Finsen Laboratory, Rigshospitalet, Copenhagen Biocenter, Copenhagen, Denmark; and ⁶ Gråsten Rheumatism Hospital, University of Southern Denmark, Gråsten, Denmark

Requests for reprints: Julia S. Johansen, Department of Rheumatology Q107, Herlev Hospital, Herlev Ringvej 75, DK-2730 Herlev, Denmark. Phone: 45-44884243; Fax: 45-44884214. E-mail: julia.johansen{at}post3.tele.dk

Serum YKL-40 is a potential biomarker of prognosis in cancer patients, but assessment of serum YKL-40 requires knowledge of its normal variation. In this study, we evaluated diurnal, weekly, and long-term variation in serum YKL-40 in healthy subjects using a commercial ELISA. The intra-assay coefficient of variation was 5.0% and interassay 10.2%. Systematic changes in diurnal measurements of serum YKL-40 could not be shown. Physical exercise for 20 min had no effect on serum YKL-40. The within-subject coefficient of variation, including variation over time and interassay, was 28.8% and 30.2% over a period of 2 and 3 years, and the intraclass correlation coefficients were 72.4% and 72.2%, indicating reasonable reliability of serum YKL-40 measurements. The 95% confidence limits for the difference between two measurements (same subject), including interassay variation, were a 52% reduction and a 109% increase in serum YKL-40. These studies show that relatively small variation is found in serum YKL-40 in healthy subjects. However, a single measurement of serum YKL-40 from an individual may not have a prognostic value, and serum YKL-40 alone cannot be a good biomarker for cancer because serum YKL-40 can be elevated in patients with other diseases characterized by inflammation and tissue remodeling. (Cancer Epidemiol Biomarkers Prev 2008;17(10):2603–8)

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