CTX and P1NP

Clinical Use

Establishing baseline level of osteoclast and osteoblast activity, and monitoring effective treatment.


More than 90% of organic bone matrix consists of type 1 collagen, which is preferentially synthesised in bone. P1NP is released (in trimeric form) during type 1 collagen formation and its subsequent incorporation into the bone matrix, and is thus a bone formation marker.

During normal bone metabolism, mature type 1 collagen is degraded and small fragments pass into the bloodstream and are excreted via the kidneys. In physiologically or pathologically elevated bone resorption (e.g. in older age or as a result of osteoporosis), type 1 collagen is degraded to an increased extent, and there is a corresponding rise in the level of collagen fragments in the blood. By determining the concentration of the plasma C-terminal telopeptides (CTX) resorption marker, the activity of osteoclasts can be assessed and/or monitored.

Circulating levels of total P1NP and CTX demonstrate significant changes upon anti-resorptive, as well as anabolic, therapy within a few weeks or months, respectively, from treatment start. Suboptimal responses to treatment may indicate noncompliance, or the presence of secondary causes of osteoporosis which may need investigation.

Sample requirements: EDTA plasma (CTX); serum/EDTA plasma (P1NP)
Sample volume: 0.5 mL
Specimen Requirements: CTX samples should be separated and frozen, and transported frozen; no special requirements for P1NP

SAS Centres providing CTX and P1NP analyses: