Type I collagen accounts for more than 90% of the organic matrix of bone. During renewal of the skeleton bone matrix is degraded and consequently fragments of type I collagen are released into circulation.
The resorption process can be studied in vitro by culturing bone cells on devitalised slices of bone or dentin.
The CrossLaps® for Culture (CTX-I) ELISA is based on the observation that certain C-telopeptide degradation products from type I collagen released during osteoclastic bone resorption occur in the circulation as modified di-peptides. These modified (β-isomerised) and cross-linked di-peptides (Glu-Lys-Ala-His-Asp-β-Gly-Gly-Arg) must be covalently cross-linked through the lysine residue for signal in the CrossLaps® for Culture ELISA.
This epitope is present in type I collagen of many species, including human, bovine, elephant and chicken. However, it is not present in rat and mouse.