Bone Turnover

In the past decades, the global incidence of osteoporosis has increased dramatically with rising life expectancy, and over 200 million people suffer from osteoporosis worldwide. By 2050, the global cost of osteoporosis is expected to exceed $130 billion and the annual hip fracture incidence is expected to increase to 6.3 million.^1,2 The highest risk of hip fractures are currently found in Norway, Sweden, Iceland, Denmark and the United States, but by 2050 Asia is expected to account for almost one-half of all global fractures.^3,4

/siemens/en_GLOBAL/gg_diag_FBAs/images/product_images/products_disease_states/bone_metabolism/Osteoporosis_q5.jpg

Click image to see details

Osteoporosis (“porous bone”) is a bone disease which increases the risk for fracture. It is caused by the loss of bone density from losing too much, not making enough or a combination of both. Bone metabolism is the constant process of the body removing old bone (“bone turnover”) and replacing it (“bone resorption”). These processes take place in the osteoblasts, which form new bone, and osteoclasts, which break down old bone. As long as these processes are in balance, bone mass remains on a constant level.

As a person reaches mid-life, they begin to lose bone quicker than they are able to replace it due to calcium metabolism, calcium and vitamin D deficiency, and hormonal factors, such as changes of estrogen level. Measuring proteins produced by the osteoblasts and osteoclasts provides a real-time evaluation of bone turnover, especially in the management of post-menopausal osteoporosis. Bone resorption markers can monitor progress of therapeutic interventions within a few weeks or months, whereas bone formation markers can take 6 to 12 months. This is still an improvement over bone mineral density (BMD), which can take as long as one to two years to determine the effectiveness of treatment.

Bone Turnover Measurement: Osteocalcin and Crosslinks Desoxypyridinoline

Measuring Bone Formation:
Osteocalcin

Measuring Bone Resorption:
Crosslinks Desoxypyridinoline

A protein found in the bone and dentin manufactured by the osteoblasts that binds to calcium
A highly specific marker of late stage osteoblastic activity
Elevated serum levels may occur in ostemalacia, Paget’s disease of the bone, hyperthyroidism, primary hyperparathyroidism and renal osteodystrophy
Depressed levels have been reported in hypothyroidism and during long-term cortiocosteriod therapy

A urine test that helps establish baseline bone turnover
Significantly elevated in post-menopausal women with osteoporosis than normal post-menopausal women
It monitors changes in urinary (deoxyopyridinoline) DPD excretion associated with aminobiphosphonate antiresorptive therapy
DPD is excreted unmetabolized in urine and is unaffected by diet, making it suitable for assessing resorption

1. Reginster JY, Burlet N. Osteoporosis: A still increasing prevalence. Bone. 2006 Feb;38(2 Suppl 1):S4-9.
2. Johnell O. The socioeconomic burden of fractures: today and in the 21st century. Am J Med. 1997 Aug 18;103(2A):20S-25S; discussion 25S-26S.
3. Kanis JA, Johnell O, De Laet C, Jonsson B, Oden A, Ogelsby AK. International variations in hip fracture probabilities: implications for risk assessment. J Bone Miner Res. 2002 Jul;17(7):1237-44.
4. Gullberg B, Johnell O, Kanis JA World-wide projections for hip fracture. Osteoporosis Int. 1997;7(5):407-13.