Introduction

Bone turnover markers are an established tool in the diagnosis and treatment of metabolic bone disease such as Paget's disease of bone. The measurements for these markers have improved considerably in the last few years such that their use can be considered for patients with osteoporosis. In this chapter, we will review the most recent evidence for using bone turnover markers in clinical practice, and give recommendations where they may prove helpful in the management of osteoporosis.

The markers currently in use in clinical practice are serum osteocalcin, serum bone alkaline phosphatase (BAP), urinary N-terminal telopeptide of type 1 collagen (NTx), urinary C-terminal telopeptide of type 1 collagen (CTx) and free deoxypyridinoline (Dpd). The introduction of automated analysers for these markers means that the assays can be performed reliably and should be available in any clinical chemistry laboratory.

Osteocalcin

Osteocalcin is the most abundant noncollagenous protein in bone. It has a high affinity for hydroxyapatite and its formation is vitamin K dependent. The serum sample should be separated and transported to the laboratory within 2 hours, but measurement of the intact and large N-terminal midfragment improves the stability of this marker [1].

Serum bone alkaline phosphatase

Bone alkaline phosphatase has a molecular weight of approximately 140 000 Dal and is found in the membrane of osteoblasts. It is released into the circulation during bone formation. This marker is very stable and is not affected by haemolysis.