@drsuefowler, i actually think your BTMs look quite reassuring. Your falling P1NP could reflect the anabolic signal from Tymlos wearing off, as well as the expected coupling effect as estrogen suppresses resorption.

By comparison, my CTX were all under 120 and P1Np under 20 during my 2nd year on HRT (i'm using the same E2 dose as you). Most recently, 86 and 15. I take that as suggesting my bone tissue is quite sensitive to estrogen's effect, and that HRT is doing what we would hope during maintenance - quieting down bone turnover. That said, I'll let DXA make the final call.

To my knowledge, there is no scientifically validated target P1NP/CTX ratio for holding onto bone gains. Dr. Eastell and colleagues have published numerous BTM analyses for antiresorptives as well as anabolics, including in the well-known ACTIVE trial of abaloparatide. They had both CTX and P1NP available and, rather than taking the ratio of the two, they developed a more complicated calculation - an "uncoupling index" - using data from ACTIVE trial. That makes me wonder, if a simple ratio were a particularly informative measure, wouldn't that have been an obvious low-hanging fruit analysis to try?

You probably know that SR was never approved in US. In Europe, its use has been restricted because of increased risks of venous thromboembolism and cardiovascular events. SC is an OTC dietary supplement with no efficacy or safety evidence for OP. Would adding SC confound the very monitoring you are relying on - particularly DXA, and possibly BTM? From what i've read, there is no reliable way to correct DXA for SC without knowing bone strontium content. I think this is a good discussion point with your doctor, as it may affect your future therapy decisions.