Clinical Information

Procollagen type I propeptides are derived from collagen type I, the most common collagen in mineralized bone. In bone, collagen is synthesized by osteoblasts in the form of procollagen, a precursor that contains a short signal sequence and terminal extension peptides: amino-terminal propeptide (PINP) and carboxy-terminal propeptide. These propeptide extensions are removed by specific proteinases before the collagen molecules form. Both propeptides circulate in blood, and their concentrations reflect the rate of collagen type I synthesis. Although collagen type I propeptides may also originate from other tissues, including skin, vessels, fibrocartilage, and tendons, most nonskeletal tissues exhibit a slower turnover than bone and contribute very little to the circulating pool of PINP. PINP is considered the most sensitive marker of bone formation and is particularly useful for monitoring bone formation and antiresorptive therapies. Testing is recommended at baseline before osteoporosis therapy begins and again 3 to 6 months later.