The C-telopeptide is an octapeptide corresponding to the C-terminus region (aa 1207-1214) of the alpha-1 chain of type 1 collagen. The presence of the C-telopeptide in urine samples is a good marker of osteoclast-mediated bone resorption observed in osteoporosis, Paget's disease, primary hyperparathyroidism, renal insufficiency and bone metastases.H-Glu-Lys-Ala-His-Asp-Gly-Gly-Arg-OH or H-EKAHDGGR-OH