schoknot26, P1NP and CTX both are serum labs. The "approved" use is to determine if a medication is working for you. Doug Lucas has two interesting videos. I like to add don't buy anything.

I'm happy that you are asking your doctor. If they refuse you can order them from https://www.jasonhealth.com/, but your insurance won't pay for them.
Item code Item Name Item Price
qt16609 Procollagen Type I Intact N Terminal Propeptide $80.00
qt17406 Collagen Type I C-Telopeptide (CTx) $50.00
Lab Collection Fee $18.00
Grand Total $148.00