title: Biological variability of serum and urinary N-telopeptides of type I collagen in postmenopausal women.
abstract: Measurement of N-telopeptides of type I bone collagen (NTX) provides a specific indicator of the current level of bone resorption. The biological intrasubject variability of NTX in urine and serum was studied in 277 postmenopausal women, mean age, 63.6 years +/- 10.2 (+/-SD) years. Second-morning void urine and serum specimens were collected at baseline and for two consecutive days to determine short-term variability (% CV). Long-term variability was determined by comparing NTX results at baseline and two consecutive months. Subjects were instructed to maintain current diet, lifestyle, and medications during the study. The median short-term %CV was 13.1% for urine NTX. This compared with 6.3% for serum NTX. Calculation of long-term %CV showed similar trends, with the %CV for NTX measured in serum (7.5%) lower than when measured in urine (15.6%). Using the least significant change (LSC) calculation, our data show that to be 90% confident that a decrease in NTX after initiation of antiresorptive therapy in an individual patient is not caused by variability alone, a 31 % decrease in urine NTX and a 14% decrease in serum NTX is required. As reported changes in NTX caused by antiresorptive therapy are greater than these calculations; our results support the use of either specimen to measure NTX to monitor the effect of therapy.
authors.affiliation: University of Sheffield, UK.
authors.forename: R
authors.initials: R
authors.lastname: Eastell
authors.forename: N
authors.initials: N
authors.lastname: Mallinak
authors.forename: S
authors.initials: S
authors.lastname: Weiss
authors.forename: M
authors.initials: M
authors.lastname: Ettinger
authors.forename: M
authors.initials: M
authors.lastname: Pettinger
authors.forename: D
authors.initials: D
authors.lastname: Cain
authors.forename: K
authors.initials: K
authors.lastname: Fressland
authors.forename: C
authors.initials: C
authors.lastname: Chesnut
mesh_terms: D000368:Aged; D015519:Bone Density; D003094:Collagen / Q000032:analysis* / Q000097:blood / Q000652:urine; D024042:Collagen Type I; D004032:Diet; D015914:Estrogen Replacement Therapy; D015444:Exercise; D005260:Female; D014644:Genetic Variation; D006801:Humans; D008019:Life Style; D008875:Middle Aged; D015663:Osteoporosis, Postmenopausal / Q000453:epidemiology / Q000235:genetics; D010455:Peptides / Q000032:analysis* / Q000097:blood / Q000652:urine; D017698:Postmenopause / Q000097:blood / Q000378:metabolism* / Q000652:urine; D012307:Risk Factors; D012907:Smoking / Q000453:epidemiology; D044465:White People
chemical_list: D024042:Collagen Type I; D010455:Peptides; C052929:collagen type I trimeric cross-linked peptide; D003094:Collagen