Measurements of molecules of bone resorption or formation can be used for estimating the rate of bone turnover. Bone turnover, as assessed by several bone metabolic markers, has been reported to undergo a diurnal rhythm. Thus far, urinary pyridinoline and deoxypyridinoline, serum osteocalcin, bone specific alkaline phosphatase, serum type I collagen cross-linked N-telopeptides (NTx), the C-terminal pyridinoline cross-linked telopeptide of type I collagen, and urinary excretion of NTx were reported to undergo circadian periodicities with high values at night (1)(5). Degradation products derived from a sequence (EKAHD-β-GGR) specific for a part of the C-telopeptide α1-chain of type I collagen (CTx) in urine and serum could be quantified by the enzyme-linked immunosorbent assay, CrossLapsTM. It had been demonstrated that such fragments are sensitive markers of bone resorption (6)(8). The purpose of this study was to determine whether there are diurnal fluctuations in the concentration of CTx in serum; if this proves true, it is important to specify the time of blood sampling.
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Wichers et al. (1999) studied this question.
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