bayhorse, bone markers are generally used after the first couple of months of a new osteoporosis medication to determine if a medication is working in your body. While there is usually a large sometimes 100% rise in P1NP after two months of an anabolic, the change at one month with bisphosphonates is usually a 30 to 50% drop in CTX.
A lack of change might initiate an effort to determine a secondary cause of osteoporosis or the need for a different medication.
CTX with Prolia decreases rapidly usually to below baseline in the first month of use. Decrease in P1NP is slower, but also significant.
Many endocrinologist don't use bone markers.
There is speculation that there might be an ideal relationship between CTX and P1NP. I speculate myself, but the closest I've read is that there needs to be a balance.