title: Reference intervals and biological variation for kallikrein 6: influence of age and renal failure.
abstract: BACKGROUND
  Kallikrein 6 (KLK6) is a serine protease involved in numerous cellular processes, up-regulated in many cancers and associated with some neurodegenerative disorders. The aim of this study was to establish a reference interval and estimate the biological variation of KLK6 in serum samples of adults. Furthermore, levels of this protein in patients with renal failure were also studied.
  
  
  METHODS
  Serum samples from healthy volunteers (n=136) were collected. Between 15 and 18 additional samples from four of these subjects were obtained over a period of 2 months. Samples from individuals (n=1043) who visited the University Health Network for a routine check-up were collected to study the association between KLK6 with age and gender. Samples from patients with renal failure (n=106) were also obtained and KLK6 and creatinine concentrations were analyzed by ELISA and an automated enzymatic method, respectively.
  
  
  RESULTS
  The reference interval was established to be 1.04-3.93 ng/mL. The index of individuality was 0.43 and the reference change value was 35%. Only two serum samples would be required to estimate the homeostatic setting point of an individual. There is a weak but highly significant positive correlation between KLK6 and age (p<0.0001). Furthermore, there is a significant positive correlation between serum concentrations of KLK6 and creatinine (p<0.0001), in patients with renal failure.
  
  
  CONCLUSIONS
  The established reference interval for KLK6 and the estimation of its biological variation will further aid in the clinical use of this protein as a serum marker of malignancy and other diseases.
authors.affiliation: Samuel Lunenfeld Research Institute, Joseph and Wolf Lebovic Health Centre, Mount Sinai Hospital, Toronto, ON, Canada.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Martínez-Morillo
authors.forename: Anastasia
authors.initials: A
authors.lastname: Diamandis
authors.forename: Eleftherios P
authors.initials: EP
authors.lastname: Diamandis
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001774:Blood Chemical Analysis / Q000592:standards*; D005260:Female; D006801:Humans; D007610:Kallikreins / Q000097:blood*; D008297:Male; D008875:Middle Aged; D010949:Plasma / Q000737:chemistry; D012016:Reference Values; D051437:Renal Insufficiency / Q000097:blood*; D044967:Serum / Q000737:chemistry; D055815:Young Adult
chemical_list: C103551:KLK6 protein, human; D007610:Kallikreins