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Reference intervals for bone turnover markers and their association with incident hip fractures in older men: the Health in Men study.

CONTEXT
Reference intervals for bone turnover markers (BTMs) and relationships between BTM and fracture risk in older men are not well characterized.


OBJECTIVE
The purpose of this article was to determine the reference intervals for serum total osteocalcin (tOC), undercarboxylated osteocalcin (ucOC), N-terminal propeptide of type I collagen (PINP), and collagen type I C-terminal cross-linked telopeptide (CTX-I) in healthy older men and to explore factors associated with BTMs, including hip fracture risk.


PARTICIPANTS AND SETTING
We studied a population-based cohort of 4248 men aged 70 to 89 years, 4008 of whom had serum samples available for analysis.


INTERVENTIONS
Morning blood samples were collected at the study visit. Comorbid conditions were assessed by questionnaire. The reference sample comprised fasting men (n = 298, median age 75.3 years [interquartile range 73.9-78.1 years) reporting excellent or very good health, without a history of diabetes, cardiovascular disease, cancer, depression, or dementia.


MAIN OUTCOME MEASURES
Serum tOC, PINP, and CTX-I were estimated by automated electrochemiluminescence immunoassays, ucOC was estimated using hydroxyapatite binding, and incident hip fractures were captured from hospital admission data.


RESULTS
Reference intervals for tOC, ucOC, PINP, and CTX-I were 10.2 to 41.0, 5.2 to 21.9, 18 to 129 μg/L, and 117 to 740 ng/L, respectively. tOC, ucOC and CTX-I were associated with hip fracture incidence, but after adjustment for other risk factors only tOC remained significantly associated.


CONCLUSIONS
Reference intervals for BTMs in older men have been defined. tOC may be more informative for hip fracture risk in older men than CTX-I and PINP. Further studies are needed to clarify the utility of BTM reference intervals in the management of aging men at risk of osteoporosis.