Hi Sue,
P1NP and CTX are fragments left in the blood by osteoblasts and osteoclasts, the cells that build and the cells that breakdown bone. Measuring those fragments tells how much bone is being cleared and how much is being replaced. They are commonly used to determine if a medication is working successfully for your bones. With teriparatide Forteo, you expect to see a large increase in the number P1NP after two or three months.