Is the predictive power of previous fractures for new spine and non-spine fractures associated with biochemical evidence of altered bone remodelling? The EPOS study. European Prospective Osteoporosis Study

Biochemical Markers of Bone Turnover and Fracture Prediction

Low bone mineral density is a strong risk factor for fractures in the older woman. Biochemical markers of bone turnover may predict fracture risk independently of bone mineral density. High levels of bone resorption markers are associated with increased risk of fracture in both retrospective and prospective studies, although the evidence for bone formation markers and fracture risk is equivocal. For example, the risk of fracture is increased up to two-fold in women with elevated levels of several markers of bone resorption. Prediction models have been developed to predict the 10–year risk of fracture using bone mineral density and biochemical markers of bone turnover and these could prove very useful in clinical practice.

The predictive role of bone turnover markers for BMD in middle-aged men

Measurement of bone turnover markers has been proposed as a potentially valuable clinical laboratory aid in osteoporosis risk assessment. These markers may allow quantitative evaluation of rates of bone loss, and thereby identify persons at risk for osteoporosis at an earlier stage. As far as we know, this is the longest longitudinal study on bone turnover markers conducted in adult men. The objectives of this study were to determine whether markers of bone formation (type I procollagen amino-terminal propeptide, PINP, and carboxy-terminal propeptide, PICP), and of bone resorption (type I collagen carboxy-terminal telopeptide, ICTP), are predictive of changes in lumbar spine and femoral neck BMD over a 5-year period, and to determine the ability of the bone resorption marker urine amino-terminal telopeptide (NTx) to explain the variance in BMD change over the past 5 years in a group of men 35-69 years old. In this group, NTx was the only marker to correlate significantly with BMD changes at the femoral neck (r = -0.21), but not at the spine. The use of the biochemical markers studied to predict change in bone density in adult men in middle-aged years is of very limited value.

The use of biochemical markers in osteoporosis

Osteoporosis is a skeletal disease in which there is a loss of, or de-crease in, bone mass with a deterioration of the microarchitecture of bone tissue. The disease is progressive, taking place over a period of years, and involves derangements in the processes of bone turnover. These derangements can be classified as those in which osteoclast activity (resorption) is stimulated so that more bone is re-moved than formed or in which osteoblast activity (formation) is hindered such that refilling of the resorption cavity is incomplete. Regardless of the process, a key pathologic development is the net loss of bone mass. This article reviews the use of biochemical markers in osteoporosis.

Collagen turnover in bone diseases

PURPOSE OF REVIEW

The primary aim of this review is to highlight recent advances in techniques available for assessing collagen turnover, particularly in relation to the diagnosis and management of bone disorders. As collagen is the major protein constituent of bone, its metabolites form the basis of most of the biochemical markers, but their efficacy needs to be viewed in the context of other non-collagenous markers, for which methodology is also advancing rapidly.

RECENT FINDINGS

New markers of bone metabolism have been developed utilising the age-dependent isomerisation and racemisation of aspartyl residues at the C-terminal end of collagen. These methods allow measurement of the ratio between newly synthesised and mature collagen: this ratio appears to provide a novel indicator of the fracture risk for osteoporosis. Other studies have led to an improved understanding of biological variability, particularly in relation to the effects of feeding. Bone resorption assays have been applied to a wide range of diseases and have been especially useful in monitoring the efficacy of novel therapies.

SUMMARY

New assays have been developed to facilitate better monitoring of collagen metabolism in bone diseases. A more complete understanding of biological variability, particularly the effects of feeding, have led to improved clinical applicability of these assays in detecting disease and monitoring therapy. Part of the future challenge, however, is to ensure that commercial assay developments keep pace with clinical expectations.