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Urinary Osteocalcin as a Marker of Bone Metabolism

¹ Institute of Biomedicine, Department of Anatomy, and ³ Department of Biotechnology, University of Turku, Turku, Finland.
² Department of Orthopaedics, Malmö University Hospital, Malmö, Sweden.

^aAddress correspondence to this author at: Institute of Biomedicine, Department of Anatomy, University of Turku, Kiinamyllynkatu 10, FI-20520 Turku, Finland. Fax 358-2-333-7352; e-mail kaisa.ivaska{at}utu.fi.

Background: Osteocalcin (OC) is produced by osteoblasts during bone formation, and circulating OC has been used in clinical investigations as a marker of bone metabolism. OC is excreted into urine by glomerular filtration and can be found in urine as midmolecule fragments.

Methods: We developed and evaluated three immunoassays (U-MidOC, U-LongOC, and U-TotalOC) for the detection of various molecular forms of urine OC (U-OC). We evaluated the association of U-OC with other markers of bone turnover and with bone mass in 1044 elderly women and studied seasonal and circadian variation of U-OC.

Results: U-OC correlated with other bone turnover markers [Spearman correlation (r), 0.30–0.57; P <0.0001], demonstrating the association between U-OC and skeletal metabolism. There was also a significant association between bone metabolism assessed by U-OC quartiles and bone mass assessed by total body bone mineral content (P <0.0001). The seasonal effects appeared to be rather small, but we observed a significant circadian rhythm similar to the one reported for serum OC with high values in the morning and low values in the afternoon.

Conclusions: The three immunoassays had unique specificities toward different naturally occurring U-OC fragments. U-OC concentrations measured with any of these assays correlated with bone turnover rates assessed by conventional serum markers of bone metabolism. The measurement of OC in urine samples could be used as an index of bone turnover in monitoring bone metabolism.

The following articles in journals at HighWire Press have cited this article:

				K. K. Ivaska, J. Lenora, P. Gerdhem, K. Akesson, H. K. Vaananen, and K. J. Obrant Serial Assessment of Serum Bone Metabolism Markers Identifies Women with the Highest Rate of Bone Loss and Osteoporosis Risk J. Clin. Endocrinol. Metab., July 1, 2008; 93(7): 2622 - 2632. [Abstract] [Full Text] [PDF]

				M. E. Kraenzlin Biochemical Markers of Bone Turnover and Osteoporosis Management IBMS BoneKEy, July 1, 2007; 4(7): 191 - 203. [Abstract] [Full Text] [PDF]

				K. K. Ivaska, K. Pettersson, A. Nenonen, K. Uusi-Rasi, A. Heinonen, P. Kannus, and H. K. Vaananen Urinary Osteocalcin Is a Useful Marker for Monitoring the Effect of Alendronate Therapy Clin. Chem., December 1, 2005; 51(12): 2362 - 2365. [Full Text] [PDF]