title: Plasma YKL-40 levels in healthy subjects from the general population.
abstract: BACKGROUND
  Plasma YKL-40 is a new biomarker in patients with cancer and inflammatory diseases. High plasma YKL-40 is associated with poor prognosis. Our aim was to determine reference levels in healthy subjects.
  
  
  METHODS
  Plasma YKL-40 was determined in 3130 participants aged 20-80 years from the Danish general population, the Copenhagen City Heart Study. They had no known disease at time of blood sampling in 1991-1994 and remained healthy and alive during a 16-year follow-up period. In 644 participants, YKL-40 was measured again in samples taken 10 years after the first.
  
  
  RESULTS
  The median plasma YKL-40 was 40 μg/L (2.5-97.5% reference levels: 14-155) with no difference between sexes. YKL-40 increased exponentially with age. For age-adjusted reference levels, the YKL-40 percentile as a function of age in years and plasma YKL-40 in μg/L was derived: percentile=100/(1+(YKL-40^-3)*(1.062^age)*5000). In subjects with two YKL-40 measurements 10 years apart, the mean increase in YKL-40 was 1.5 μg/L/year (SE: 0.2), while the mean change in the calculated age percentile was minimal (-0.3; SE: 0.1).
  
  
  CONCLUSIONS
  Plasma YKL-40 increases with age within and across healthy individuals from the general population. Age-stratified or age-adjusted reference levels are important when YKL-40 test results are evaluated.
authors.affiliation: Department of Clinical Biochemistry, Herlev Hospital, Copenhagen University Hospital, University of Copenhagen, Denmark. stebo@heh.regionh.dk
authors.forename: Stig E
authors.initials: SE
authors.lastname: Bojesen
authors.forename: Julia S
authors.initials: JS
authors.lastname: Johansen
authors.forename: Børge G
authors.initials: BG
authors.lastname: Nordestgaard
mesh_terms: D054392:Adipokines; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000097:blood; D001774:Blood Chemical Analysis / Q000592:standards*; D000071451:Chitinase-3-Like Protein 1; D005260:Female; D006023:Glycoproteins / Q000097:blood*; D006262:Health; D006801:Humans; D037102:Lectins / Q000097:blood*; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D013997:Time Factors; D055815:Young Adult
chemical_list: D054392:Adipokines; D015415:Biomarkers; C084533:CHI3L1 protein, human; D000071451:Chitinase-3-Like Protein 1; D006023:Glycoproteins; D037102:Lectins