Article

Urinary osteocalcin as a marker of bone metabolism.

Institute of Biomedicine, Department of Anatomy, University of Turku, Turku, Finland.
Clinical Chemistry (impact factor: 7.91). 03/2005; 51(3):618-28. DOI:10.1373/clinchem.2004.043901
Source: PubMed

ABSTRACT 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.
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.
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.
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.

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Keywords

1044 elderly women
 
bone mass
 
bone turnover markers [Spearman correlation
 
bone turnover rates
 
conventional serum markers
 
immunoassays
 
low values
 
monitoring bone metabolism
 
Osteocalcin
 
serum OC
 
significant circadian rhythm
 
three immunoassays
 
total body bone mineral content
 
U-OC
 
U-OC concentrations
 
U-OC correlated
 
U-OC fragments
 
U-OC quartiles
 
urine OC
 
urine samples
 

Kaisa Ivaska