Different Behaviors of Serum and Urinary CrossLaps ELISA in the Assessment of Bone Resorption in Healthy

Many fragments derived from collagen I degradation come to serum during bone resorption. The characteriza-tion of these fragments and the development of assays that can measure them are the basis of most of the biochemical markers of bone resorption. One of these fragments consists of two cross-linked amino acid se-quences derived from the C-terminal telopeptide region of type I collagen a1 chains. Fragments containing the sequence EKAH-DGGR (CTX), with a DG site being either nonisomerized (a-CTX) or b-isomerized (b-CTX) were identified. Pyridinoline, deoxypyridinoline, and other cross-links linked both telopeptides (Fig. 1) (1). Recent reports have suggested that the proportions of non-isomerized and b-isomerized fragments depend on bone age (1)