title: Variability in urinary excretion of bone resorption markers: limitations of a single determination in clinical practice.
abstract: In this study we assessed the within and between-subject variability of the concentrations of two urinary markers, free deoxypyridinoline (DPD) and C telopeptide (CTX-I), in healthy patients with the aim of setting reliable thresholds to enable physicians to take decisions about individual patients with confidence.Between-subject variability for the women was 25.4% for DPD and 38.2% for CTX-I, and for the men was 12.9% for DPD and 23.8% for CTX-I. The coefficients of variation were similar for daily, weekly and monthly determinations, giving means of 13.8 and 28.1% for DPD and CTX-I respectively. Critical difference (CD) was lower for DPD than for CTX-I (about 44 and 80% respectively). The number of samples required to determine the true mean with a CD at the 5% level was 29 for DPD and more than 113 for CTX-I.DPD was the least biologically variable. One determination was not sufficient to determine bone resorption status and a 44% decrease in DPD levels and an 80% decrease in CTX-I levels were required to demonstrate the efficacy of antiresorptive therapy in individual patients.
authors.affiliation: Laboratoire de Biochimie A, Hôpital Cochin, 27 rue du Faubourg Saint Jacques 75014, Paris, France.
authors.forename: D
authors.initials: D
authors.lastname: Borderie
authors.forename: C
authors.initials: C
authors.lastname: Roux
authors.forename: B
authors.initials: B
authors.lastname: Toussaint
authors.forename: M
authors.initials: M
authors.lastname: Dougados
authors.forename: O G
authors.initials: OG
authors.lastname: Ekindjian
authors.forename: B
authors.initials: B
authors.lastname: Cherruau
mesh_terms: D000328:Adult; D000596:Amino Acids / Q000652:urine*; D001862:Bone Resorption / Q000652:urine*; D003094:Collagen / Q000652:urine*; D024042:Collagen Type I; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010455:Peptides / Q000652:urine*; D017697:Premenopause
chemical_list: D000596:Amino Acids; D024042:Collagen Type I; D010455:Peptides; C052929:collagen type I trimeric cross-linked peptide; C036020:deoxypyridinoline; D003094:Collagen