In bone physiology, the C-terminal telopeptide (or more formally, carboxy-terminal collagen crosslinks, and known by the acronym CTX) is a telopeptide that can be used as a biomarker in the serum to measure the rate of bone turnover. It can be useful in assisting clinicians to determine a patient's nonsurgical treatment response as well as evaluate a patient's risk of developing complications during healing following surgical intervention. The test used to detect the CTX marker is called the Serum CrossLaps, and it is more specific to bone resorption than any other test currently available.