title: Urinary osteocalcin as a marker of bone metabolism.
abstract: BACKGROUND
  Osteocalcin (OC) is produced by osteoblasts during bone formation, and circulating OC has been used in clinical investigations as a marker of bone metabolism. OC is excreted into urine by glomerular filtration and can be found in urine as midmolecule fragments.
  
  
  METHODS
  We developed and evaluated three immunoassays (U-MidOC, U-LongOC, and U-TotalOC) for the detection of various molecular forms of urine OC (U-OC). We evaluated the association of U-OC with other markers of bone turnover and with bone mass in 1044 elderly women and studied seasonal and circadian variation of U-OC.
  
  
  RESULTS
  U-OC correlated with other bone turnover markers [Spearman correlation (r), 0.30-0.57; P <0.0001], demonstrating the association between U-OC and skeletal metabolism. There was also a significant association between bone metabolism assessed by U-OC quartiles and bone mass assessed by total body bone mineral content (P <0.0001). The seasonal effects appeared to be rather small, but we observed a significant circadian rhythm similar to the one reported for serum OC with high values in the morning and low values in the afternoon.
  
  
  CONCLUSIONS
  The three immunoassays had unique specificities toward different naturally occurring U-OC fragments. U-OC concentrations measured with any of these assays correlated with bone turnover rates assessed by conventional serum markers of bone metabolism. The measurement of OC in urine samples could be used as an index of bone turnover in monitoring bone metabolism.
authors.affiliation: Institute of Biomedicine, Department of Anatomy, University of Turku, Turku, Finland. kaisa.ivaska@utu.fi
authors.forename: Kaisa K
authors.initials: KK
authors.lastname: Ivaska
authors.forename: Sanna-Maria
authors.initials: SM
authors.lastname: Käkönen
authors.forename: Paul
authors.initials: P
authors.lastname: Gerdhem
authors.forename: Karl J
authors.initials: KJ
authors.lastname: Obrant
authors.forename: Kim
authors.initials: K
authors.lastname: Pettersson
authors.forename: H Kalervo
authors.initials: HK
authors.lastname: Väänänen
mesh_terms: D000368:Aged; D015415:Biomarkers / Q000652:urine; D015519:Bone Density; D001842:Bone and Bones / Q000378:metabolism*; D002940:Circadian Rhythm; D005260:Female; D006801:Humans; D007118:Immunoassay; D015675:Osteocalcin / Q000652:urine*; D012016:Reference Values; D012621:Seasons; D012680:Sensitivity and Specificity; D013048:Specimen Handling; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013696:Temperature
chemical_list: D015415:Biomarkers; D015675:Osteocalcin