Osteoporosis Investigations

Bone Turnover Markers
Heel – Quantitative Ultrasound (QUS)
Interpretation of DEXA Measures

Bone Turnover Markers

As bone is a dynamic organ, it is possible to assess its activity by measurement of bone turnover markers. Biochemical markers of bone turnover are divided into 2 groups: formation markers (eg. serum alkaline phosphatase, serum osteocalcin, serum procollagen I carboxy-terminal extension peptides and serum procollagen I animo-terminal extension peptides) and resorption markers (eg. urinary collagen cross-links, urinary type I collagen N and C-telopeptides, serum free pyridinoline and deoxypyridinoline, serum type I collagen N and C-telopeptide breakdown products and tartrate-resistant acid phosphatase).

Measurement of bone turnover markers either in serum or urine, are not routinely performed as part of assessment for osteoporosis. However, they are independent predictors of fracture in addition to BMD measures. The EPIDOS study which was a large study of elderly French women, showed that elevated baseline markers of bone resorption (urinary C-telopeptide and free deoxypyridinoline crosslinks) was predictive of an increased risk of hip fracture during 2 years of follow up. In addition if increased bone resorption markers were coupled with an initial low bone density measure, then the predictive value of future hip fracture was even greater, than either measure alone.⁵⁷ The finding of low bone mineral density and increased markers of bone resorption, may assist with treatment decisions with regards to commencing therapy for individual women, even in the absence of fracture.

The other potential role for bone turnover markers is to monitor the success of therapy with various treatments for osteoporosis. Several studies have shown that treatment with hormone therapy, bisphosphonates and parathyroid hormone, is associated with a significant change in bone turnover markers usually within 3 – 6 months of initiating therapy.^58-61 Favourable changes in bone turnover markers at 3 or 6 months after initiating therapy, has also been found to be a valid predictor of improved bone mineral density at 2 years.^58,60,62,63 More recent studies have shown the reduction in bone resorption marker levels comprises a large component of the anti-fracture efficacy of bisphosphonates.⁶³ Thus, early improvements in bone turnover markers can potentially identify individuals who are responding to treatment, particularly with anti-resorptive medication. Improvements in technology reducing the variability of anaylyte measurement in serum assays will allow more widespread clinical use of these assays in the future.

Heel – Quantitative Ultrasound (QUS)

Quantitative ultrasound of the calcaneus is a frequently used tool by many women in the community to screen for osteoporosis. This is primarily due to its ready availability, particularly within pharmacies. There is no Medicare rebate for this procedure in Australia.

At this point in time DEXA remains the “gold standard” for the diagnosis of osteoporosis. However, several prospective studies have shown that calcaneal QUS can predict fracture risk in elderly women.^64,65 It’s ability to do so in men is less clear.⁶⁶ One of the major problems with calcaneal QUS is the establishment of appropriate cut-off levels with this measure, which will distinguish healthy individuals from osteoporotic individuals. ^67,68 However, low QUS measures are comparable to DEXA in detecting osteoporosis.^65,69,70 The use of QUS to monitor an individual patient on treatment for osteoporosis is also not well established.⁷¹ Currently, the use of calcaneal QUS cannot be recommended as a means to diagnose or monitor osteoporosis. However, as this technique is further evaluated, there is the potential that in the future it may have a role in the management of osteoporosis.

Content updated February 20, 2006