Bone turnover markers – harmonising measurement and reporting

Abstract

Bone turnover markers (BTMs) are classified as either formation or resorption markers and are useful in the management of patients with bone disease. The concentrations of BTM in blood or urine may provide an estimate of the rate of bone remodelling. Serum procollagen type I amino-terminal propeptide (s-PINP) and serum carboxy-terminal cross-linking telopeptide of type I collagen (s-βCTX) have been designated as reference standard markers of bone formation and resorption respectively in osteoporosis by the International Federation of Clinical Chemistry (IFCC) and the International Osteoporosis Foundation (IOF). These two BTMs show the most promise for use in osteoporosis management although more data are needed before they can be incorporated into absolute fracture risk calculators and in guidelines for monitoring treatment. Standardised patient preparation is required to minimise the effect of biological variation and appropriate handling and storage are important for sample stability. Inter-method differences for BTM assays are well recognised, and harmonisation of methods for the reference markers is being jointly undertaken by IFCC and IOF. This will facilitate the development of universally accepted decision limits and treatment goals. Australian consensus reference intervals for adults have been developed for some methods for s-total PINP and s-βCTX based on published data. Agreement has also been achieved for reporting units. The premenopausal adult female reference intervals are 15–70 μg/L for s-total PINP, and 150–800 ng/L for s-CTX (Roche Diagnostics). Separate reference intervals apply for postmenopausal females and for adult males of different age groups.