Serum CrossLaps for monitoring the response in individuals undergoing antiresorptive therapy.

The Serum CrossLaps (CTx) enzyme-linked immunosorbent assay (ELISA) is specific for a cross-linked, beta-aspartate-isomerized form of the epitope EKAHDGGR derived from the carboxyterminal telopeptide region of type I collagen alpha(1) chain. Collagen type I fragments reactive in the CTx assay are released during osteoclastic bone resorption and can be used as a measure of bone resorption activity. Our objectives were to assess the intraindividual variation of serum CTx concentration as well as the clinical value of the serum CTx assay for monitoring antiresorptive therapy in individual patients.