title: Critical differences in the serial measurement of three biochemical markers of bone turnover in the sera of pre- and postmenopausal women.
abstract: OBJECTIVE
  The purpose of this investigation was to quantify the biologic, day-to-day variability and critical differences in serum levels of crosslinked collagen N-telopeptides (NTx), procollagen aminoterminal extension propeptides (PINP) and bone specific alkaline phosphatase (bAP) in healthy women.
  
  
  METHODS
  Seven blood samples were collected from 12 pre- and 15 postmenopausal women over 4 to 6 months. NTx, PINP and bAP levels were determined utilizing enzyme- and radioimmunoassay techniques.
  
  
  RESULTS
  The within-subject coefficient of variation (C.V.) in serum bAP, NTx and PINP levels was 7.1, 10.6 and 12.4% respectively. These variances did not differ significantly among premenopausal women when compared with postmenopausal subjects. Combining terms for analytical and biologic variability revealed that a critical difference between 2 successive serial measurements is 24% for bAP, 34% for NTx and 38% for PINP.
  
  
  CONCLUSIONS
  Circulating levels of NTx, PINP and bAP are stable over time periods of several months, allowing for the determination of significant changes in skeletal metabolism of women.
authors.affiliation: Medical Laboratory Sciences, Department of Pathology, HSSB Room 220, University of New Mexico School of Medicine, Albuquerque, New Mexico 87131-5651, USA. Jscariano@salud.unm.edu
authors.forename: J K
authors.initials: JK
authors.lastname: Scariano
authors.forename: P J
authors.initials: PJ
authors.lastname: Garry
authors.forename: G D
authors.initials: GD
authors.lastname: Montoya
authors.forename: J M
authors.initials: JM
authors.lastname: Wilson
authors.forename: R N
authors.initials: RN
authors.lastname: Baumgartner
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000469:Alkaline Phosphatase / Q000097:blood*; D015415:Biomarkers / Q000097:blood; D001862:Bone Resorption / Q000097:blood* / Q000000981:diagnostic imaging; D003094:Collagen / Q000097:blood*; D024042:Collagen Type I; D005260:Female; D006801:Humans; D008875:Middle Aged; D010446:Peptide Fragments / Q000097:blood*; D010455:Peptides / Q000097:blood*; D017698:Postmenopause / Q000502:physiology*; D017697:Premenopause / Q000502:physiology*; D011347:Procollagen / Q000097:blood*; D013997:Time Factors; D014463:Ultrasonography
chemical_list: D015415:Biomarkers; D024042:Collagen Type I; D010446:Peptide Fragments; D010455:Peptides; D011347:Procollagen; C052929:collagen type I trimeric cross-linked peptide; C047202:procollagen Type I N-terminal peptide; D003094:Collagen; D000469:Alkaline Phosphatase